My point is that he was using force to compel the states to remain in the Union, not to end slavery. He wasn’t sending his army out with the mission of freeing the slaves, which is most likely what my high school civics class was teaching.
While Lincoln hated slavery he also respected the rule of law, at least occasionally, and he repeatedly said that he didn’t have the authority to order slaves to be set free. He eventually did it as a war measure affecting only the States which were in rebellion, which of course the British had also done during the American Revolution. But slaves in the states that remained loyal to the Union remained slaves.
Frederick Douglass did a good job of describing Lincoln’s opinion of blacks and slavery in a speech he gave on the 10th anniversary of Lincoln’s death. Douglass knew Lincoln personally. Douglass said that he and his fellow blacks were afterthoughts in Lincoln’s decisions. And while he was eternally grateful for what Lincoln did he harbored no illusions that the war or any other great decisions made by Lincoln were done with blacks first and foremost in his mind.
No, Lincoln was using US military to defeat the aggressor force which had first provoked, then started and declared war on the United States.
Freeing slaves became a key strategic weapon in Lincoln's plan for victory, because it not only weakened the Confederacy, but also helped meet Radical Republican abolitionist goals.