Answer:
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.
Step-by-step 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.