Answer:
There are many arguments for and against secession but in 1869 the Supreme Court of the United States said it was legal to secede from the Union if after you seceded you became and maintained your separate independence. This was the Supreme Court saying everyone was right. The Confederacy could secede but the Union could legally force them back into the Union by force and the Confederacy had to do whatever it had to do to maintain the secession. What the war proved was that the Union army could go wherever it wanted and do whatever it wanted to and could legally force the Cofederacy back into the Union.