True until mid -1862. Then he came to realize that the ONLY way to save the Union was to eliminate slavery, for the Confederacy’s sole purpose in existence was to protect slavery, and 2/3 of the South’s population was feeding and arming the 1/2 who were fighting.
Superb new book on the leadup to war and the war itself by Oakes, “Freedom National,” who showed how northern abolitionists figured out (correctly) that the Constitution doesn’t mention slaves, only unfree PERSONS, and that by emphasizing the personhood of slaves they could end it OR force the South to go to war to defend slavery, when they could end it.
They had a brilliant plan.
Lincoln urged the passage of the Corwin amendment which would have guaranteed slavery indefinitely.
Those who believe the war was about slavery have been successfully fooled by the propaganda apparatus of the DC rulers.
The war was about money that would be lost to the powerful industrialists of the North if the South seceded.
It was about nothing other than that threatened loss of money to the crony capitalists of that era.