Was Lincoln Justified In Prosecuting A War Justified?

As of today i didn't really know all this about Lincoln, now knowing all this Lincoln is no justified in prosecuting the war the way he did, that the only beneficial thing that came out of this war even for his own benefits was the freedom of many slaves, which they are human beings, and knowing the worse was the many slave that die because they were the one in combat was a disaster. Is very in human to see how people use power to get what they want not caring about the harm that will cause others. Like the professor says,"he didn’t fight the war to free the slaves. Instead, he freed some of the slaves to help fight the war." all Lincoln did was to be beneficiary of doing that, and by doing that he already had all the slaves on his side, cause