The change in the South during Reconstruction that most likely resulted in the rise of organizations such as the Ku Klux Klan was that African Americans gained more rights and influence in society.
The establishment of rights for African Americans, such as voting and holding office, led to a backlash among some white Southerners who felt threatened by this newfound power and sought to restore white supremacy through violence and intimidation, culminating in the formation of groups like the Ku Klux Klan.