The Civil War was about secession.
Secession was about slavery.
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The problem is that the troops who actually fought on the ground could not care less about slavery or the “black issue”.
If Lincoln had said in 1861 “we are fighting a war to end slavery” he would have had to raise an army to kidnap civilians to fight the war.
A myth we have all be3en taught but which doesn't stand up to the light of scrutiny.
The Corwin amendment alone proves that slavery had nothing to do with why the North invaded the South.
The real reason was money. Specifically 700 million per year in trade with Southern goods that the North controlled and wanted to continue controlling.
Had the South just wanted "slavery", they would have taken the Crowin amendment deal. What they wanted was to control their own economy and control their own trade.