Suspicions of immigrants, Catholics, and modernists contributed to a string of reactionary organizations. None so captured the imaginations of the country as the reborn Ku Klux Klan (KKK), a white supremacist organization that expanded beyond its Reconstruction Era anti-black politics to now claim to protect American values and way of life from blacks, feminists (and other radicals), immigrants, Catholics, Jews, atheists, bootleggers, and a host of other imagined moral enemies.

Two events in 1915 are widely credited with inspiring the rebirth of the Klan: the lynching of Leo Frank and the release of The Birth of the Nation, a popular and groundbreaking film that valorized the Reconstruction Era Klan as a protector of feminine virtue and white racial purity. Taking advantage of this sudden surge of popularity, Colonel William Joseph Simmons organized what is often called the “second” Ku Klux Klan in Georgia in late 1915. This new Klan, modeled after other fraternal organizations with elaborate rituals and a hierarchy, remained largely confined to Georgia and Alabama until 1920, when Simmons began a professional recruiting effort that resulted in individual chapters being formed across the country and membership rising to an estimated five million.

Partly in response to the migration of Southern blacks to Northern cities during World War I, the KKK expanded above the Mason-Dixon. Membership soared in Philadelphia, Detroit, Chicago, and Portland, while Klan-endorsed mayoral candidates won in Indianapolis, Denver, and Atlanta. The Klan often recruited through fraternal organizations such as the Freemasons and through various Protestant churches. In many areas, local Klansmen would visit churches of which they approved and bestow a gift of money upon the presiding minister, often during services. The Klan also enticed people to join through large picnics, parades, rallies, and ceremonies. The Klan established a women’s auxiliary in 1923 headquartered in Little Rock, Arkansas. The Women of the Ku Klux Klan mirrored the KKK in practice and ideology and soon had chapters in all forty-eight states, often attracting women who were already part of the prohibition movement, the defense of which was a centerpiece of Klan activism.

Contrary to its perception of as a primarily Southern and lower-class phenomenon, the second Klan had a national reach composed largely of middle-class people. Sociologist Rory McVeigh surveyed the KKK newspaper Imperial Night-Hawk for the years 1924 and 1924, at the organization’s peak, and found the largest number of Klan-related activities to have occurred in Texas, Pennsylvania, Indiana, Illinois, and Georgia. The Klan was even present in Canada, where it was a powerful force within Saskatchewan’s Conservative Party. In many states and localities, the Klan dominated politics to such a level that one could not be elected without the support of the KKK. For example, in 1924, the Klan supported William Lee Cazort for governor of Arkansas, leading his opponent in the Democratic Party primary, Thomas Terral, to seek honorary membership through a Louisiana klavern so as not to be tagged as the anti-Klan candidate. In 1922, Texans elected Earle B. Mayfield, an avowed Klansman who ran openly as that year’s “klandidate,” to the United States Senate. At its peak the Klan claimed between four and five million members.

Despite the breadth of its political activism, the Klan is today remembered largely as a violent vigilante group—and not without reason. Members of the Klan and affiliated organizations often carried out acts of lynching and “nightriding”—the physical harassment of bootleggers, union activists, civil rights workers, or any others deemed “immoral” (such as suspected adulterers) under the cover of darkness or while wearing their hoods and robes. In fact, Klan violence was extensive enough in Oklahoma that Governor John C. Walton placed the entire state under martial law in 1923. Witnesses testifying before the military court disclosed accounts of Klan violence ranging from the flogging of clandestine brewers to the disfiguring of a prominent black Tulsan for registering African Americans to vote. In Houston, Texas, the Klan maintained an extensive system of surveillance that included tapping telephone lines and putting spies into the local post office in order to root out “undesirables.” A mob that organized and led by Klan members in Aiken, South Carolina, lynched Bertha Lowman and her two brothers in 1926, but no one was ever prosecuted: the sheriff, deputies, city attorney, and state representative all belonged to the Klan.

The Klan dwindled in the face of scandal and diminished energy over the last years of the 1920s. By 1930, the Klan only had about 30,000 members and it was largely spent as a national force, only to appear again as a much diminished force during the civil rights movement in the 1950s and ’60s.