I'm aware of why the Confederate States succeeded from the Union, but why did the Union launch a campaign to take it back?

In the beginning of the U.S. we had the Articles of Confedaration. This was a loose organization of states where the power of the federal government was incredibly weak it couldn’t tax or have a standing army. This was because the colonists were terrified of tyranny like they faced under the British. This government functioned okay with some things, passed the Ordinance of 1785 and the Northwest Ordinance. A rebellion happened in Massachusetts. It was called Shays rebellion and the feds got lucky and the state was able to put it down. This helped them realize the important for a strong federal government capable of controlling the states. I mean up until this point

/r/AskHistorians Thread