Events of World War I



The Alliances

During the 19th century, the major European powers went to great lengths to maintain a balance of power throughout Europe, resulting in the existence of a complex network of political and military alliances throughout the continent leading up to World War I. According to some historians, this caused a localized conflict to escalate into a global war.

Learning Objectives

Name the members of the two alliances that clashed in WWI

Key Takeaways

Key Points

  • Starting directly after the Congress of Vienna in 1815, the Great Powers of Europe began to forge complex alliances to maintain a balance of power and peace.
  • This process began with the Holy Alliance between Prussia, Russia, and Austria and the Quadruple Alliance signed by United Kingdom, Austria, Prussia, and Russia, both formed in 1815 and aimed at maintaining a stable and conservative vision for Europe.
  • Throughout the rest of the 19th century, various treaties and alliances were formed, including the German-Austrian treaty (1879) or Dual Alliance; the addition of Italy to the Germany and Austrian alliance in 1882, forming the ” Triple Alliance “; the Franco-Russian Alliance (1894); and the ” Entente Cordiale ” between Britain and France (1904), which eventually included Russia and formed the Triple Entente.
  • The Triple Alliance and the Triple Entente, which were renewed several times leading up to World War I, formed the two opposing sides of the war, with Italy moving over to ally with the Triple Entente after the start of the war and other nations pulled in over time.
  • Historians debate how much these complex alliances contributed to the outbreak of the World War I, as the crisis between Austria-Hungary and Serbia could have been localized but quickly escalated into a global conflict despite the fact that some of the alliances, notably the Triple Entente, did not stipulate mutual defense in the case of an attack.

Key Terms

  • Triple Alliance: A secret agreement between Germany, Austria-Hungary, and Italy formed on May 20, 1882, and renewed periodically until World War I. Germany and Austria-Hungary had been closely allied since 1879. Italy sought support against France shortly after it lost North African ambitions to the French. Each member promised mutual support in the event of an attack by any other great power.
  • Triple Entente: The informal understanding linking the Russian Empire, the French Third Republic, and the United Kingdom of Great Britain and Ireland after the signing of the Anglo-Russian Entente on August 31, 1907. The understanding between the three powers, supplemented by agreements with Japan and Portugal, constituted a powerful counterweight to the Triple Alliance of Germany, Austria-Hungary, and the Kingdom of Italy.
  • Central Powers: Consisting of Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria, this was one of the two main factions during World War I (1914–18). It faced and was defeated by the Allied Powers that formed around the Triple Entente, after which it was dissolved.

During the 19th century, the major European powers went to great lengths to maintain a balance of power throughout Europe, resulting in the existence of a complex network of political and military alliances throughout the continent by 1900. These began in 1815 with the Holy Alliance between Prussia, Russia, and Austria. When Germany was united in 1871, Prussia became part of the new German nation. In October 1873, German Chancellor Otto von Bismarck negotiated the League of the Three Emperors between the monarchs of Austria-Hungary, Russia, and Germany. This agreement failed because Austria-Hungary and Russia could not agree over Balkan policy, leaving Germany and Austria-Hungary in an alliance formed in 1879 called the Dual Alliance. This was a method of countering Russian influence in the Balkans as the Ottoman Empire continued to weaken. This alliance expanded in 1882 to include Italy, in what became the Triple Alliance.

Bismarck held Russia at Germany’s side to avoid a two-front war with France and Russia. When Wilhelm II ascended to the throne as German Emperor (Kaiser), Bismarck was compelled to retire and his system of alliances was gradually de-emphasized. For example, the Kaiser refused in 1890 to renew the Reinsurance Treaty with Russia. Two years later, the Franco-Russian Alliance was signed to counteract the force of the Triple Alliance. In 1904, Britain signed a series of agreements with France, the Entente Cordiale, and in 1907, Britain and Russia signed the Anglo-Russian Convention. While these agreements did not formally ally Britain with France or Russia, they made British entry into any future conflict involving France or Russia a possibility, and the system of interlocking bilateral agreements became known as the Triple Entente.

Interestingly, family connections pervaded these alliances, some crossing the boundaries of opposition. Kaiser Wilhelm II of Germany, King George V of England, and Tsar Nicholas II of Russia were cousins.

Central Powers

The Central Powers, consisting of Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria – hence also known as the Quadruple Alliance – was one of the two main factions during World War I (1914–18). It faced and was defeated by the Allied Powers that formed around the Triple Entente, after which it was dissolved.

The Central Powers consisted of the German Empire and the Austro-Hungarian Empire at the beginning of the war. The Ottoman Empire joined the Central Powers later in 1914. In 1915, the Kingdom of Bulgaria joined the alliance. The name “Central Powers” is derived from the location of these countries; all four (including the other groups that supported them except for Finland and Lithuania) were located between the Russian Empire in the east and France and the United Kingdom in the west. Finland, Azerbaijan, and Lithuania joined them in 1918 before the war ended and after the Russian Empire collapsed.

The Central Powers’ origin was the Triple Alliance. Also known as the Triplice, this was a secret agreement between Germany, Austria-Hungary, and Italy formed on May 20, 1882, and renewed periodically until World War I. Germany and Austria-Hungary had been closely allied since 1879. Italy sought support against France shortly after it lost North African ambitions to the French. Each member promised mutual support in the event of an attack by any other great power. The treaty provided that Germany and Austria-Hungary would assist Italy if it was attacked by France without provocation. In turn, Italy would assist Germany if attacked by France. In the event of a war between Austria-Hungary and Russia, Italy promised to remain neutral.

Shortly after renewing the Alliance in June 1902, Italy secretly extended a similar guarantee to France. By a particular agreement, neither Austria-Hungary nor Italy would change the status quo in the Balkans without previous consultation. On November 1, 1902, five months after the Triple Alliance was renewed, Italy reached an understanding with France that each would remain neutral in the event of an attack on the other.

When Austria-Hungary found itself at war in August 1914 with the rival Triple Entente, Italy proclaimed its neutrality, considering Austria-Hungary the aggressor and defaulting on the obligation to consult and agree compensations before changing the status quo in the Balkans as agreed in 1912 renewal of the Triple Alliance. Following parallel negotiation with both Triple Alliance, aimed to keep Italy neutral, and the Triple Entente, aimed to make Italy enter the conflict, Italy declared war on Austria-Hungary. Carol I of Romania, through his Prime Minister Ion I. C. Brătianu, also secretly pledged to support the Triple Alliance, but he remained neutral since Austria-Hungary started the war.

Allies of WWI

The Allies of World War I were the countries that opposed the Central Powers in the First World War.

The members of the original Entente Alliance of 1907 were the French Republic, the British Empire, and the Russian Empire. Italy ended its alliance with the Central Powers, arguing that Germany and Austria-Hungary started the war and that the alliance was only defensive in nature; it entered the war on the side of the Entente in 1915. Japan was another important member. Belgium, Serbia, Greece, Montenegro, and Romania were affiliated members of the Entente.

The 1920 Treaty of Sèvres defines the Principal Allied Powers as the British Empire, French Republic, Italy, and Japan. The Allied Powers comprised, together with the Principal Allied Powers, Armenia, Belgium, Greece, Hejaz, Poland, Portugal, Romania, Serb-Croat-Slovene state, and Czechoslovakia.

The U.S. declaration of war on Germany in April 1917 was on the grounds that Germany had violated its neutrality by attacking international shipping and the Zimmermann Telegram sent to Mexico. It declared war on Austria-Hungary in December 1917. The U.S. entered the war as an “associated power,” rather than as a formal ally of France and the United Kingdom to avoid “foreign entanglements.” Although the Ottoman Empire and Bulgaria severed relations with the United States, neither declared war.

European diplomatic alignments shortly before the war, depicted as a series of Venn diagrams overlapping where treaties or support was established.

Web of Alliances: European diplomatic alignments shortly before the outbreak of WWI.

The Schlieffen Plan

The Schlieffen Plan was a deployment plan and operational guide for a decisive initial offensive campaign in a one-front war against the French Third Republic. In 1914 it was deployed against two fronts with major changes by Commander-in-Chief Moltke the Younger, resulting in a failure to achieve the decisive victory Schlieffen had planned.

Learning Objectives

Describe the Schlieffen Plan

Key Takeaways

Key Points

  • Alfred von Schlieffen was a German field marshal and strategist who served as Chief of the Imperial German General Staff from 1891 to 1906.
  • Throughout his career, he developed several war plans for defensive, offensive, and counter-offensive campaigns, particularly with the French.
  • The offensive campaign against France developed in 1905-06, later termed the “Schleiffen Plan,” focused on a brute force attack with sufficient soldiers.
  • When Schlieffen retired, Helmuth von Moltke the Younger took over a Commander-in-Chief of the German army and at the outbreak of WWI, deployed a modified version of Schlieffen’s plan against the latter’s advice, which failed to achieve the decisive victory it promised.
  • Various historians have contended that Moltke the Younger’s failure to follow the blueprint rather than German strategic miscalculation condemned the belligerents to four years of attrition warfare.

Key Terms

  • counter-offensive: A term used by the military to describe large-scale, usually strategic offensive operations by forces that successfully halt the enemy’s offensive while occupying defensive positions. It is executed after exhausting the enemy’s front line troops when their reserves are committed to combat and incapable of breaching defenses, but before the enemy has had the opportunity to assume new defensive positions.
  • Alfred von Schlieffen: A German field marshal and strategist who served as Chief of the Imperial German General Staff from 1891 to 1906. His name lived on in the 1905-06 Schlieffen Plan, then Aufmarsch I, a deployment plan and operational guide for a decisive initial offensive campaign in a one-front war against the French Third Republic.

The Schlieffen Plan was the strategy for the German invasion of France and Belgium in August 1914. Field Marshal Alfred von Schlieffen was the Chief of the Imperial Army German General Staff from 1891 to 1906 and in 1905-06 devised a deployment plan for a winning offensive in a one-front war against the French Third Republic. After the war, German historians and other writers described the plan as a blueprint for victory. Some claimed the plan was ruined by Colonel-General Helmuth von Moltke the Younger, the Commander-in-Chief of the German army after Schlieffen retired in 1906 who was dismissed after the First Battle of the Marne (September 5-12, 1914).

Alfred von Schlieffen’s War Planning

The cornerstone of Schlieffen’s war planning was undoubtedly the strategic counter-offensive. Schlieffen was a great believer in the power of the attack in the context of the defensive operation. Germany’s smaller forces relative to the Franco-Russian Entente meant that an offensive posture against one or both was basically suicidal. On the other hand, Schlieffen placed great faith in Germany’s ability to use railways to launch a counter-offensive against a hypothetical French or Russian invasion force, defeat it, then quickly regroup and launch a counter-offensive.

Schlieffen also recognized the need for offensive planning, as failing to do so would limit the German Army’s capabilities. In 1897, Schlieffen developed a tactical plan that – acknowledging the German army’s limited offensive power and capacity for strategic maneuvers – basically amounted to using brute force to advance beyond the French defenses on the Franco-German border.

In 1905, Schlieffen developed what was truly his first plan for a strategic offensive operation, the Schlieffen plan Denkschrift (Schlieffen plan memorandum). This was designed for an isolated Franco-German war that would not involve Russia, calling for Germany to attack France.

However, the bulk of Schlieffen’s planning followed his personal preferences for the counter-offensive. Schlieffen’s war plans by the name of Aufmarsch II and Aufmarsch Ost continued to stress that Germany’s best hope for survival in a war with the Franco-Russian entente was a defensive strategy. This was reconciled with a very offensive tactical posture as Schlieffen held that the destruction of an attacking force required that it be surrounded and attacked from all sides until surrender, not merely repulsed as in a passive defense.

In August 1905 Schlieffen was kicked by a companion’s horse, rendering him incapable of battle at age 72. He began planning his retirement, but his successor was undetermined. A favourite of the Emperor was Helmuth von Moltke the Younger, who became Chief of Staff after Schlieffen retired.

Moltke went on to devise Aufmarsch II Ost, a variant on Schlieffen’s Aufmarsch Ost designed for an isolated Russo-German war. Schlieffen seemingly tried to impress upon Moltke that an offensive strategy against France could only work in the event of an isolated Franco-German war, as German forces would otherwise be too weak to implement it. Knowing this, Moltke still attempted to apply the offensive strategy of Aufmarsch I West to the two-front war Germany faced in 1914 and Schlieffen’s defensive plan Aufmarsch II West. With too few troops to cross west of Paris let alone attempt a crossing of the Seine, Moltke’s campaign failed to breach the French “second defensive sector” and his troops were pushed back in the Battle of the Marne.

Post-war writing by senior German officers like Hermann von Kuhl, Gerhard Tappen, Wilhelm Groener, and official historians led by the former Lieutenant-Colonel Wolfgang Förster established a commonly accepted narrative that it was Moltke the Younger’s failure to follow the blueprint rather than German strategic miscalculation that condemned the belligerents to four years of attrition warfare instead of the quick, decisive conflict it could have been.

Deployment of the Schlieffen Plan

At the outbreak of World War I, 80% of the German army was deployed as seven field armies in the west according to the plan Aufmarsch II West. However, they were then assigned to execute the retired deployment plan Aufmarsch I West, from the Schlieffen Plan. This would march German armies through northern Belgium and into France in an attempt to encircle the French army and breach the “second defensive area” of the fortresses of Verdun and Paris and the Marne river.

Aufmarsch I West was one of four deployment plans available to the German General Staff in 1914. Each favored certain operations but did not specify exactly how those operations would be carried out, leaving the commanding officers to do so at their own initiative with minimal oversight. Aufmarsch I West, designed for a one-front war with France, was retired once it became clear it was irrelevant to the wars Germany could expect to face. Both Russia and Britain were expected to help France with no possibility of assistance from Italian or Austro-Hungarian troops. But despite its unsuitability and the availability of more sensible and decisive options, it retained a certain allure due to its offensive nature and the pessimism of pre-war thinking, which expected offensive operations to be short-lived, costly in casualties, and unlikely to be decisive. Accordingly, the Aufmarsch II West deployment was changed for the offensive of 1914, despite its unrealistic goals and the insufficient forces Germany had available for decisive success. Moltke took Schlieffen’s plan and modified the deployment of forces on the western front by reducing the right wing, the one to advance through Belgium, from 85% to 70%. In the end, the Schlieffen plan was so radically modified by Moltke that it could be more properly called the Moltke Plan.

Germany attacked Luxembourg on August 2 and on August 3 declared war on France. On August 4, after Belgium refused to permit German troops to cross its borders into France, Germany declared war on Belgium as well. Britain declared war on Germany on the same day following an “unsatisfactory reply” to the British ultimatum that Belgium must be kept neutral.

In the end, Germany failed to avoid a long, two-front war, but had fought its way into a good defensive position inside France and effectively halved France’s supply of coal. It had also killed or permanently crippled 230,000 more French and British troops than it itself had lost. Despite this, communications problems and questionable command decisions cost Germany the chance of a more decisive outcome.

A map of Europe in 1914 showing the possible route of the Schlieffen plan with red dotted lines.

Schlieffen Plan: One historian’s depiction of the Schlieffen Plan in red dotted lines.

Early Battles

Following the outbreak of war in August 1914, the German Army opened the Western Front by invading Luxembourg and Belgium, but were forced back with the Battle of the Marne.

Learning Objectives

Summarize the general trends of the early battles of World War I

Key Takeaways

Key Points

  • The Western Front was the main theatre of war during World War I.
  • Following the outbreak of war in August 1914, the German Army opened the Western Front by invading Luxembourg and Belgium, then gained military control of important industrial regions in France.
  • These early German offensives include the Battle of Liège and the Battle of the Frontiers at the border of France.
  • The tide of the advance was dramatically turned with the Battle of the Marne, in which French and British troops were able to force a German retreat by exploiting a gap between the 1st and 2nd Armies, ending the German advance into France.
  • The resulting “Race to the Sea” had both sides establishing a meandering line of fortified trenches stretching from the North Sea to the Swiss frontier with France in an attempt to outflank the opposition.
  • This line remained essentially unchanged for most of the war.

Key Terms

  • First Battle of the Marne: Also known as the Miracle of the Marne, this World War I battle fought in September 1914 resulted in an Allied victory against the German Army. The battle was the culmination of the German advance into France and pursuit of the Allied armies that followed the Battle of the Frontiers in August and reached the eastern outskirts of Paris. A counter-attack by six French field armies and the British Expeditionary Force (BEF) along the Marne River forced the Imperial German Army to retreat northwest, leading to the Battle of the Aisne and the “Race to the Sea.” The battle was a victory for the Allies, but also set the stage for four years of trench warfare stalemate on the Western Front.
  • Battle of the Frontiers: A series of battles along the eastern frontier of France and in southern Belgium shortly after the outbreak of World War I. The battles resolved the military strategies of the French Chief of Staff General Joseph Joffre with Plan XVII and an offensive interpretation of the German Aufmarsch II deployment plan by Helmuth von Moltke the Younger. The Franco-British forces were driven back by the Germans, who were able to invade northern France. French and British rearguard actions delayed the German advance and thus allowed the French time to transfer their forces to the west to defend Paris, resulting in the First Battle of the Marne.
  • Siege of Liège: The opening engagement of the German invasion of Belgium and the first battle of World War I. The attack on Liège city began on August 5, 1914, and lasted until August 16 when the last fort surrendered. The length of the siege of Liège may have delayed the German invasion of France by 4–5 days.

Battle of Liège

At the outbreak of the First World War, the German Army (consisting in the west of seven field armies) executed a modified version of the Schlieffen Plan, designed to quickly attack France through neutral Belgium before turning southwards to encircle the French Army on the German border. Belgium’s neutrality was guaranteed by Britain under the 1839 Treaty of London; this caused Britain to join the war at the expiration of its ultimatum at 11 p.m. GMT on August 4, 1914, when armies under German generals Alexander von Kluck and Karl von Bülow attacked Belgium. Luxembourg had been occupied without opposition on August 2. The first battle in Belgium was the Siege of Liège, which lasted from August 5-16. Liège was well-fortified and surprised the German Army under von Bülow with its level of resistance. Nonetheless, German heavy artillery was able to demolish the main forts within a few days. Following the fall of Liège, most of the Belgian field army retreated to Antwerp, leaving the garrison of Namur isolated, with the Belgian capital, Brussels, falling to the Germans on August 20. Although the German army bypassed Antwerp, it remained a threat to their flank. Another siege followed at Namur, lasting from about August 20-23.

For their part, the French had five armies deployed on their borders. The pre-war French offensive plan, Plan XVII, intended to capture Alsace-Lorraine following the outbreak of hostilities. On August 7 the VII Corps attacked Alsace with the objective to capture Mulhouse and Colmar. The main offensive was launched on August 14 with 1st and 2nd Armies attacking toward Sarrebourg-Morhange in Lorraine. In keeping with the Schlieffen Plan, the Germans withdrew slowly while inflicting severe losses upon the French. The French advanced the 3rd and 4th Armies toward the Saar River and attempted to capture Saarburg, attacking Briey and Neufchateau, before being driven back. The French VII Corps captured Mulhouse after a brief engagement on August 7, but German reserve forces engaged them in the Battle of Mulhouse and forced a French retreat.

Battle of the Frontiers

The German Army swept through Belgium, executing civilians and razing villages. The application of “collective responsibility” against a civilian population further galvanized the allies, and newspapers condemned the German invasion and the army’s violence against civilians and property, together called the “Rape of Belgium.” After marching through Belgium, Luxembourg, and the Ardennes, the German Army advanced in the latter half of August into northern France, where they met the French Army under Joseph Joffre and the initial six divisions of the British Expeditionary Force under Sir John French. A series of engagements known as the Battle of the Frontiers ensued, which included the Battle of Charleroi and the Battle of Mons. In the former battle the French Fifth Army was almost destroyed by the German 2nd and 3rd Armies and the latter delayed the German advance by a day. A general Allied retreat followed, resulting in more clashes at the Battle of Le Cateau, the Siege of Maubeuge, and the Battle of St. Quentin (also called the First Battle of Guise).

First Battle of the Marne

The German Army came within 43 miles of Paris but at the First Battle of the Marne (September 6-12), French and British troops were able to force a German retreat by exploiting a gap that appeared between the 1st and 2nd Armies, ending the German advance into France. The German Army retreated north of the Aisne River, establishing the beginnings of a static western front that would last for the next three years. Following this German retirement, the opposing forces made reciprocal outflanking maneuvers known as the Race for the Sea and quickly extended their trench systems from the Swiss frontier to the North Sea. The territory occupied by Germany held 64 percent of French pig-iron production, 24 percent of its steel manufacturing, and 40 percent of the coal industry, dealing a serious blow to French industry.

Laying Trenches and the First Battle of Ypres

On the Entente side (those countries opposing the German alliance), the final lines were occupied by the armies of the Allied countries, with each nation defending a part of the front. From the coast in the north, the primary forces were from Belgium, the British Empire, and France. Following the Battle of the Yser in October, the Belgian army controlled a 22-mile length of West Flanders along the coast known as the Yser Front, along the Yser river and the Yperlee canal from Nieuwpoort to Boesinghe. Stationed to the south was the sector of the British Expeditionary Force (BEF).

From October 19 until November 22, the German forces made their final breakthrough attempt of 1914 during the First Battle of Ypres. Heavy casualties were suffered on both sides but no breakthrough occurred. After the battle, Erich von Falkenhayn judged that it was no longer possible for Germany to win the war and on November 18 called for a diplomatic solution, but Chancellor Theobald von Bethmann-Hollweg, Paul von Hindenburg and Erich Ludendorff disagreed.

Map of the Western Front and the Race to the Sea, 1914

Stabilization of the Western Front WWI: Map of the Western Front and the Race to the Sea, 1914

Trench Warfare

After the German march on Paris was halted at the First Battle of the Marne, both sides dug in along a meandering line of fortified trenches stretching from the North Sea to the Swiss frontier with France. The Western Front settled into a battle of attrition, with a trench line that changed little until 1917.

Learning Objectives

Analyze why trench warfare became such a defining feature of World War I

Key Takeaways

Key Points

  • Trench warfare is a type of land warfare with occupied fighting lines consisting largely of trenches in which troops are significantly protected from the enemy’s small arms fire and sheltered from artillery. The most famous use of trench warfare is the Western Front in World War I.
  • Trench warfare occurs when a revolution in firepower is not matched by similar advances in mobility, as in the first two decades of the 20th century when advances allowed the creation of strong defensive systems that out-of-date military tactics could not break through for most of the war.
  • Barbed wire was a significant hindrance to massed infantry advances. Artillery vastly more lethal than in the 1870s, coupled with machine guns, made crossing open ground extremely difficult.
  • Commanders on both sides failed to develop tactics for breaching entrenched positions without heavy casualties, resulting in such major battles as the Battle of the Somme, which cost the British Army some 420,000 casualties, the French an estimated 200,000 casualties, and the Germans an estimated 500,000.
  • In time, however, technology began to produce new offensive weapons, such as gas warfare and the tank, but it was only after the adoption of improved tactics that some degree of mobility was restored.

Key Terms

  • Race to the Sea: The term described reciprocal attempts by the Franco-British and German armies to envelop the northern flank of the opposing army through Picardy, Artois, and Flanders, rather than an attempt to advance northwards to the sea. The “race” ended on the North Sea coast of Belgium around October 19, when the last open area from Dixmude to the North Sea was occupied by Belgian troops who had been withdrawn from the Siege of Antwerp (September 28 – October 10). The outflanking attempts resulted in a number of encounter battles, but neither side was able to gain a decisive victory.
  • Battle of the Somme: A battle of the First World War fought by the armies of the British and French empires against the German Empire. It took place between July 1 and November 18, 1916, on both sides of the upper reaches of the River Somme in France. The battle was intended to hasten a victory for the Allies and was the largest battle of the First World War on the Western Front. More than one million were wounded or killed, making it one of the bloodiest battles in human history.
  • Trench warfare: A type of land warfare using occupied fighting lines consisting largely of trenches, in which troops are significantly protected from the enemy’s small arms fire and sheltered from artillery.

Trench Warfare in World War I

Trench warfare occurs when a revolution in firepower is not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender holds the advantage. Military tactics developed before World War I failed to keep pace with advances in technology and became obsolete. These advances had allowed the creation of strong defensive systems, which out-of-date military tactics could not break through for most of the war. Barbed wire was a significant hindrance to massed infantry advances, while artillery vastly more lethal than in the 1870s, coupled with machine guns, made crossing open ground extremely difficult. Commanders on both sides failed to develop tactics for breaching entrenched positions without heavy casualties. In time, however, technology began to produce new offensive weapons, such as gas warfare and the tank.

On the Western Front in 1914–18, both sides constructed elaborate trench and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, and other obstacles. The area between opposing trench lines (known as “no man’s land”) was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.

Just after the First Battle of the Marne (September 5-12, 1914), Entente and German forces repeatedly attempted maneuvering to the north in an effort to outflank each other, a strategy that became known as the “Race to the Sea.” When these outflanking efforts failed, the opposing forces soon found themselves facing an uninterrupted line of entrenched positions from Lorraine to Belgium’s coast Britain. France sought to take the offensive while Germany defended the occupied territories. Consequently, German trenches were much better constructed than those of their enemy; Anglo-French trenches were only intended to be “temporary” before their forces broke through the German defenses.

Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on March 21, 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals to be decided by attrition. The small, improvised trenches of the first few months grew deeper and more complex, gradually becoming vast areas of interlocking defensive works. They resisted both artillery bombardment and mass infantry assault. Shell-proof dugouts became a high priority. Frontal assaults and their associated casualties became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker’s massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side able to commit the last reserves to the Western Front.

Neither side delivered a decisive blow for the next two years. Throughout 1915–17, the British Empire and France suffered more casualties than Germany because of the strategic and tactical stances chosen by the sides. Strategically, while the Germans only mounted one major offensive, the Allies made several attempts to break through the German lines.

In February 1916 the Germans attacked the French defensive positions at Verdun. Lasting until December 1916, the battle saw initial German gains before French counter-attacks returned them near their starting point. Casualties were greater for the French, but the Germans bled heavily as well, with anywhere from 700,000 to 975,000 casualties suffered between the two combatants. Verdun became a symbol of French determination and self-sacrifice.

The Battle of the Somme was an Anglo-French offensive of July to November 1916. The opening of this offensive (July 1, 1916) saw the British Army endure the bloodiest day in its history, suffering 57,470 casualties, including 19,240 dead, on the first day alone. The entire Somme offensive cost the British Army some 420,000 casualties. The French suffered another estimated 200,000 casualties and the Germans an estimated 500,000.

The last large-scale offensive of this period was a British attack (with French support) at Passchendaele (July–November 1917). This offensive opened with great promise for the Allies before bogging down in the October mud. Casualties, though disputed, were roughly equal at some 200,000–400,000 per side.

These years of trench warfare in the West saw no major exchanges of territory and, as a result, are often thought of as static and unchanging. However, throughout this period, British, French, and German tactics constantly evolved to meet new battlefield challenges.

Trenches of the 11th Cheshire Regiment at Ovillers-la-Boisselle, on the Somme, July 1916. One sentry keeps watch while the others sleep.

Trench Warfare: Trenches of the 11th Cheshire Regiment at Ovillers-la-Boisselle, on the Somme, July 1916. One sentry keeps watch while the others sleep. Photo by Ernest Brooks.

Development of Advanced Weaponry

Both sides tried to break the trench stalemate using scientific and technological advances. On April 22, 1915, at the Second Battle of Ypres, the Germans (violating the Hague Convention) used chlorine gas for the first time on the Western Front. After a two-day bombardment, the Germans released a cloud of 171 tons of chlorine gas onto the battlefield. Though primarily a powerful irritant, it can asphyxiate in high concentrations or prolonged exposure. The gas crept across no man’s land and drifted into the French trenches. The green-yellow cloud killed some defenders and those in the rear fled in panic, creating an undefended 3.7 mile gap in the Allied line. The Germans were unprepared for the level of their success and lacked sufficient reserves to exploit the opening. Canadian troops on the right drew back their left flank and repelled the German advance.

The success of this attack would not be repeated, as the Allies countered by introducing gas masks and other countermeasures. The British retaliated, developing their own chlorine gas and using it at the Battle of Loos in September 1915. Fickle winds and inexperience led to more British casualties from the gas than German. Several types of gas soon became widely used by both sides, and though it never proved a decisive, battle-winning weapon, poison gas became one of the most-feared and best-remembered horrors of the war. French, British, and German forces all escalated the use of gas attacks through the rest of the war, developing the more deadly phosgene gas in 1915, then the infamous mustard gas in 1917, which could linger for days and kill slowly and painfully. Countermeasures also improved and the stalemate continued.

Tanks were developed by Britain and France, and were first used in combat by the British during the Battle of Flers–Courcelette (part of the Battle of the Somme) on September 15, 1916, with only partial success. However, their effectiveness would grow as the war progressed; the Allies built tanks in large numbers, whilst the Germans employed only a few of their own design supplemented by captured Allied tanks.