You avoided my argument about the Civil War completely :)
You do not have a democratically elected Mainland government with a constitution that both the Mainland and the island agreed to beforehand. Therefore, the island is not "breaking away" from that government with its democratically elected leaders. It's never been a part of it...and they fought the war to make sure they were not a part of it...and they are not to this day. In essence, the mainland is fighting a war of agression to MAKE the island become a part of something it never has had, and never wanted to have anything to do with...a mainland communist government.
Completely different scenario than the American civil war.