It all started when the south broke away from the North because the south wanted to keep slaves and the north wanted them to be freed.
So it started a war. If the north won, slaves will be freed and they have to come back. But if the south won they would keep slaves.
They even elected a leader of the south
The union troops first thought they could win the war quickly, but failed.
The war would determine what would happen to the US of A.
The US won the war.