But do you know WHY?
The north also had slaves. However, the cities of the north relied on funding from the Federal government for their welfare programs carried over from England. However, the Fed was running out of money and needed more taxes to keep things going. In order to get more taxes, the North cooked up the idea that cotton farmers and other southern slave owners would have to pay taxes on each slave as though they were a free man. The south rejected this, eventually leading to the 3/5ths compromise. But, the north continued to push, and since the southern citizens weren't going to pay such exorbitant taxes, the north decided to outlaw slavery in the south while allowing the slave owners in the north to retain their slaves and not pay extra taxes on them.
The Democrats then formed a Coalition becoming the Confederate States of America and declared Secession. Following the war, Lincoln, who believed in "absolute" emancipation, seized the moment and freed all the slaves, which he wasn't supposed to do.
It was never "We, the compassionate non-slave owners of the north must free those poor Negro slaves of the south!".
It was literally just a re-run of the War of Rebellion, except this time the separatists lost.
Which lead to the Democrats funding the Reconstruction era KKK, followed by the Democrats enacting Jim Crow laws across the south "to protect white jobs", followed by "The New Deal", until the success of the Civil Rights Movement of the 1960's, at which time the Democrats pivoted to holding black people down via government aid programs. But Blacks were out reproducing Whites, leading to the introduction of 'Planned Parenthood" in the 1980's, along with Affirmative Action programs to maintain resentment amongst Whites. Then the Democrats signed the legislation that allowed sub-prime mortgages in the 90's along with the growth of BET, and in the late 2000's "no child left behind" was retooled into the affirmative funding that keeps Blacks overcrowded in schools despite a declining birth rate, leading into Black Lives Matter because "White Republicans just aren't doing enough for us" and aided by Obama's eternal race baiting, which brings us to today.