“The war was caused by the North treating the South like a colony”

The South was not treated as a colony to be exploited, it’s federal laws were the same for it as at any other point in the country.

“using it’s numerical advantages to pass laws that transfered wealth from the South to the North.”

Turn about’s fair play–the South had been using its artificial electoral advantage (the 3/5ths compromise, when it should have been 0/5ths), to advance slaveholding interest since the Founding. The South betrayed the Founders by not abolishing slavery in the first place, and they had no expectation they would get to unconstitutionally start ignoring the law when it was no longer serving their advantage.

“There is nothing in the constitution that forbids secession, therefore secession is not un-constitutional.”

As I have already explained to the confederate apologists here many times, the constitution is the law of the land, and the confederate secession was contrary to it–so it was unlawful, unconstitutional, and treason. From the 10th amendment to the supremacy clause, to the power of the president to execute the laws by the military if need be, secession was treason.

If the South had sought and gotten an amendment to the constitution to permit secession, then they would have merely been repugnant to the conscience of man and the meaning of the American Revolution, but not treasonous.