That's either utterly ignorant or a gross distortion. The idea of abolition had been around since America's founding. Just because it wasn't official policy, doesn't mean it wasn't the root cause. Lincoln was a pragmatist. When he ran he said he wouldn't interfere with slavery in states where it existed, but opposed any new slave states. The southern elites who owned the slaves and controlled southern politics didn't believe him, and in any case knew that eventually without expanding slavery into the new states they would ultimately be too small a minority to maintain slavery. So they seceded before Lincoln was even sworn in.
Being a pragmatist Lincoln's first goal was to save the union. He said if he could save it by freeing all the slaves he would, if he could save it by freeing none he would, and if he could save it by freeing some and leaving others he would. He also knew if he issued the emancipation proclamation after a string of southern victories it would look like desperation. So he waited until after the union victory at Antietam to do so. That's a far cry form not raising the idea before 1863.
The emancipation proclamation did not free a single slave in the United States. None. The border states that didn’t join the confederacy were allowed to remain as slave states. It applied only to the rebel states and since they were no longer part of the United States, the proclamation meant nothing to any slave in either the north or the south.
” The idea of abolition had been around since America’s founding. “
Before the founding. The British government announced two emancipation declarations during our war of independence.
The blacks they freed ended up in Canada after the Crown failed to suppress the secession of 1776. Lincoln wasn’t the first to wage a war to force rebels to remain in a union that they wanted out of, and he wasn’t the first to emancipate slaves. Slavery in America would have been over 90 years earlier if we had lost the fight for independence.
So Lincoln was for slavery before he was against slavery. Typical scummy politician.