> black people here were actively denied their rights that the civil war was supposed to have guaranteed them.

The Civil War was not supposed to have guaranteed anyone any rights.

Some changes to the Constitution rammed through after the Civil War were, but it's important to separate those from the war, which was about the objective that, even before the rebellion, the notionally-abolitionist Republicans expressly put ahead of treating blacks as humans, the preservation of the unity of the Republic.