Formed in 1865 as a “secret lodge” by former Confederates in Pulaski, Tennessee, the Invisible Empire or Ku Klux Klan (KKK) has been and remains committed to white supremacy in America.

Klansmen, beside other diehard groups, violently resisted Reconstruction. Still defending the South, they fought Union Army occupation, Republican governments, and blacks’ freedom. Donning hoods and using secret titles, they took an oath to defend Christianity, the Constitution, and the white race, especially their women's purity. Loyal to the Democratic Party, the Klan enlisted men and women from all classes. Targeting Union Leagues (freedmen's political clubs), night riders harassed and often killed black and Republican voters and officeholders, burned black churches and schools, intimidated teachers, and stole elections. In the 1868 elections, alongside Knights of the White Camellia, they murdered 1,000 black and white Republicans in Louisiana alone. After its investigation, Congress passed the Ku Klux Act (1871). But undermanned Union garrisons rarely stopped the Klan's plunder. Its terrorism during the election of 1876 hastened Reconstruction's end.

Between 1877 and 1910 the KKK fueled Democrats’ push to establish one-party rule and Jim Crow. A coalition of Democrats, Klansmen, Red Shirts, Rifle Clubs, and White Leagues targeted freedmen and their allies, utilizing ballot fraud, intimidation, and murder. Some 1,751 blacks were lynched in southern and border states ca. 1882–1900 as black and white farmers’ alliances and the Populist Party coalesced for reform. Defeat of populists by ballot-rigging and terror enabled Democrats, as the Supreme Court instituted the “separate but equal” rule, to enact Jim Crow. The system disfranchised and terrorized blacks; it also persecuted Jews, Catholics, and nonwhite immigrants.

Klan people promoted white racism in the twentieth century. Early on they enlisted members with The Birth of a Nation (1915), a film glorifying the Klan's bloody defeat of Reconstruction. By the mid-1920s, the second KKK claimed several million members in more than a dozen states. Affiliates were strong in the Midwest (being more anti-Catholic and anti-immigrant there) than in the South. State and local Klans frequently attacked progressives prior to the Civil Rights Act of 1957, which ensured the right to vote.