This was the withdrawal of eleven southern states from the union in 1860 that precipitated the american civil war.

Secession

Explanation:

Secession was the withdrawal of eleven southern states from the union in 1860 that precipitated the American civil war. These 11 states were states  in which slave holding was legal, they were majorly Southern states. They seceded after the election of Abraham Lincoln in 1860, and this led to the civil war.