Why did the Ku Klux Klan threaten African Americans during
Reconstruction?

Klan was an alliterative version of "clan," thus Ku Klux Klan suggested a circle, or band, of brothers. With the passage of the Military Reconstruction Acts in March 1867, and the prospect of freedmen voting in the South, the Klan became a political organization.

Explanation:

on the morning of  july 21,  1861, general mcdowell ordered the  unionarmy to attack. it was on this hill that  confederate  colonel thomas jackson and his forces held back theunion  troops.

c. the passage of the fifteenth amendment