The Oregon Treaty

A fervent belief in expansion gripped the United States in the 1840s. As previously stated, in 1845, New York newspaper editor, John O’Sullivan, introduced the concept of “manifest destiny” to describe the popular idea of the special role of the United States in overtaking the continent. Manifest Destiny asserted the divine right and duty of White Americans to seize and settle the American West, thus spreading Protestant, democratic values. In this climate of opinion, voters in 1844 elected James K. Polk, a slaveholder from Tennessee, because he vowed to annex Texas as a new slave state and obtain the Oregon Country solely for the U.S., as it had been shared with Great Britain since 1818.

Annexing Oregon was an important objective for U.S. foreign policy because it appeared to be an area rich in commercial possibilities. Northerners favored U.S. control of Oregon because ports in the Pacific Northwest would be gateways for trade with Asia. Southerners hoped that, in exchange for their support of expansion into the Northwest, Northerners would not oppose plans for expansion into the Southwest.

Figure 1. This map of the Oregon territory during the period of joint occupation by the United States and Great Britain shows the area whose ownership was contested by the two powers.

President Polk—whose campaign slogan in 1844 had been “Fifty-four forty or fight!”—asserted the United States’ right to gain full control of what was known as Oregon Country, from its southern border at 42° latitude (the current boundary with California) to its northern border at 54° 40′ latitude. According to the Treaty of 1818, Great Britain and the United States held joint ownership of this territory, but the 1827 Treaty of Joint Occupation opened the land to settlement by both countries. Realizing that the British were not willing to cede all claims to the territory, Polk proposed the land be divided at 49° latitude (the current border between Washington and Canada). The British, however, denied U.S. claims to land north of the Columbia River (Oregon’s current northern border). Indeed, the British foreign secretary refused even to relay Polk’s proposal to London. However, reports of the difficulty Great Britain would face defending Oregon in the event of a U.S. attack, combined with concerns over affairs at home and elsewhere in its empire, quickly changed the minds of the British, and in June 1846, Queen Victoria’s government agreed to a division at the forty-ninth parallel. The U.S. too had its own problems to deal with, as the Mexican-American War had broken out in April 1846. Both countries knew that another war between them was not worth the cost, and so the treaty was signed without incident.

In contrast to the diplomatic solution with Great Britain over Oregon, when it came to Mexico, President Polk and the American people proved willing to use force to obtain more land for the United States.

The Annexation of Texas

Texas annexation had remained a political landmine since the Republic declared independence from Mexico in 1836. American politicians feared that adding Texas to the Union would provoke a war with Mexico and reignite sectional tensions by throwing off the balance between free and slave states. However, after his expulsion from the Whig party, President John Tyler (James Polk’s predecessor) saw Texas statehood as the key to saving his political career. In 1842, he began presenting annexation as a national debate. Harnessing public outcry over the issue, Democrat James K. Polk rose from virtual obscurity to win the presidential election of 1844. Polk and his party campaigned on promises of westward expansion, with eyes toward Texas, Oregon, and California.

In keeping with voters’ expectations, President Polk set his sights on the Mexican state of California. After the mistaken capture of Monterey, negotiations about purchasing the port of San Francisco from Mexico broke off until September 1845. Polk also made overtures about purchasing Upper California and New Mexico as well, which went nowhere. The Mexican government, angered by U.S. actions, refused to recognize the independence of Texas because they felt that the U.S. had helped Texas to rebel so that they could claim the territory for themselves (which was mostly true). In the final days of his presidency in March 1845, President Tyler had extended an official offer of statehood to Texas. The Republic accepted the offer on July 4th, and President Polk officially agreed in December 1845, making Texas the newest slave state.

Mexico’s Reaction

Incensed that the United States had annexed Texas, the Mexican government refused to discuss the matter of selling land to them, including California, which Polk desperately wanted. Indeed, Mexico refused even to acknowledge Polk’s emissary, John Slidell, who had been sent to Mexico City to negotiate the sale of California for $25 million. Not to be deterred, Polk encouraged Thomas O. Larkin, the U.S. consul in Monterey, to assist any American settlers and any Californios, the Mexican residents of the state, who wished to proclaim their independence from Mexico. By the end of 1845, Mexico had broken diplomatic ties with the United States over Texas and was growing increasingly alarmed by American actions in California. The Mexican government warily anticipated the Americans’ next move and it did not have long to wait.