The Ku Klux Klan (KKK) is an extremist hate group in the United States. It was founded shortly after the United States Civil War ended. It used intimidation, violence, and murder to maintain white supremacy in Southern government and social life.

Late in 1865, just after the Civil War ended, the KKK was founded. The Klan, a secret organization that used terror tactics to target newly freed African Americans, attracted defeated Confederates who resented the changes of Reconstruction. Under the cloak of darkness and in disguise, the KKK worked to enforce white supremacy as the political and social order of the South.

The end of the Civil War brought freedom to enslaved African Americans in the former Confederacy. The 14th and 15th Amendments to the Constitution, as well as federal laws introduced during the years of Reconstruction (1866–1877), were intended to protect the civil rights of freed people. However, when they tried to exercise their new rights, they encountered intimidation and violence, much of it organized by the Klan.

The votes of formerly enslaved men helped give control of the Mississippi state legislature to the Republican Party, which made Hiram Rhodes Revels the first African American in the United States Senate. In 1870, South Carolina directly elected Joseph Rainey, another African American, to the U.S. House of Representatives. The Klan reacted with terrorizing night rides to the homes of black voters.

Throughout the South, lynching and intimidation were prevalent. The KKK used secrecy, intimidation, violence, and murder to prevent formerly enslaved African-American men from voting. Black officeholders and their supporters were especially targeted.

In 1871, during the presidency of Ulysses S. Grant, anti-Klan laws were passed allowing the president to declare martial law. Grant did not use these powers to the full extent of the law, but some state militias did break up Klan chapters. Nine South Carolina counties were placed under martial law and arrests followed.

However, after Reconstruction ended in 1877, state legislatures were able to put in place Jim Crow laws that ensured white superiority and segregation. Black voters were intimidated or simply blocked from registering and voting. The new laws placed almost insurmountable obstacles in the way of voting. The early Klan disbanded in the 1870s, partly because of federal laws but also because its goals had been met. The Klan would be revived in the early 20th century with its falsely heroic portrayal in The Birth of a Nation film. The influx of Catholic and Jewish immigrants from Eastern Europe offered a new target for the Klan's prejudice.