The anti-black backlash after the Civil War was carried out by groups intent on restoring white supremacy and overturning Reconstruction gains. The Ku Klux Klan fits this pattern best: formed by former Confederates in the South right after the war, it quickly turned into a secret society that used threats, violence, and terror to suppress African American civic participation and intimidate supporters of Reconstruction. Their violence aimed to restore white political dominance by intimidating Black voters, teachers, and leaders, and by burning schools and churches to undermine newly won rights. Other groups mentioned are not the same era or purpose. The White League emerged a bit later in Louisiana as another white supremacist force, but it’s not the central emblem of Reconstruction-era resistance. The Sons of Liberty points to a Revolutionary-era group, long before Reconstruction, and the Liberation Party isn’t a recognized Reconstruction-era organization. So the Ku Klux Klan best embodies the anti-black reaction to Reconstruction policies.