From my poor understanding both sides had slaves but the south had the majority of them and their entire economy relied on them. The north was slowly freeing them but that didn’t mean they were actually free.

Found a very general summary here:

Beginning during the Revolution and in the first two decades of the postwar era, every state in the North abolished slavery. These were the first abolitionist laws in the Atlantic World. However, the abolition of slavery did not necessarily mean that existing slaves became free. In some states they were forced to remain with their former owners as indentured servants: free in name only, although they could not be sold and thus families could not be split, and their children were born free. The end of slavery did not come in New York until July 4, 1827, when it was celebrated (on July 5) with a big parade. However, in the 1830 census, the only state with no slaves was Vermont. In the 1840 census, there were still slaves in New Hampshire (1), Rhode Island (5), Connecticut (17), New York (4), Pennsylvania (64), Ohio (3), Indiana (3), Illinois (331), Iowa (16), and Wisconsin (11). There were none in these states in the 1850 census.

https://en.wikipedia.org/wiki/Slavery_in_the_United_States?wprov=sfti1#Abolitionism_in_the_North

Another good quote

The amendment did not take effect until it was ratified by three-fourths of the states, which occurred on December 6, 1865, when Georgia ratified it. On that date, the last 40,000–45,000 enslaved Americans in the remaining two slave states of Kentucky and Delaware, as well as the 200 or so perpetual apprentices in New Jersey left from the very gradual emancipation process begun in 1804, were freed. The last Americans known to have been born into legal slavery died in the 1970s

civil war website link

https://acwm.org/blog/myths-misunderstandings-north-and-slavery/

Slavery developed hand-in-hand with the founding of the United States, weaving into the commercial, legal, political, and social fabric of the new nation and thus shaping the way of life of both the North and the South. American attitudes to slavery were complex with much disagreement; however, before emancipation, many northerners felt guilty about slavery and white southerners expected federal protection of the “peculiar institution.” These feelings, which directly influenced many people’s choices leading to secession and Civil War in 1860-1, can only be understood by seeing slavery as a national institution.

Northerners as different as Harriett Beecher Stowe and William Henry Seward regarded slavery as a national sin rather than a southern fault. For Republican politicians in the late 1850s, the fear that slaveholders stood ready to take over the nation was real. Seward’s “Irrepressible Conflict” speech in 1858 argued how “the United States must, sooner or later, become either an entirely slaveholding nation or entirely a free-labor nation.”

Looking at the institution of slavery as “just a southern thing” obscures the conscious interdependency connected by slavery between people’s wealth and power in the North and South. Yet, slavery remained very different for the South compared with the North. For the South, slavery was never solely an economic system, but also provided the racial underpinning of southern social structures when, in 1860, 95% of African Americans lived in the South. This distinction reinforced a perception of difference believed by citizens of one section about the other, despite the many historical, cultural, and economic links of slavery between North and South.