A few things to note:
Comparing states to countries that can secede at any time they want is FACTUALLY incorrect. They are not countries. The U.S. is not the EU, where countries assist each other. A better term for the states is principalities. A state can only be founded with permission of Congress.
And to say that the Union simply conquered innocent rebels is incorrect also, because Union facilities were attacked by the CSA BEFORE the Civil War.