What did Southern states do to keep control of

slaves?

They seceded from the Union of the United States, formed their own confederate government and declared war against the United States, which was an act of treason based on our Constitution.

Explanation:

Agriculture was the southern states' primary source of collective economy, this was mainly achieved on large plantations which utilized solely slave labor. The potential loss of this way for income earning meant to many Southerners that their entire way of life was being threatened by the government, and they weren't going to allow that.

They disobey the Constitution of the United States and separated themselves from the country.

Explanation:

They did this to keep slave labor going, because they wanted power over mankind.