The economy of the northeast centered around commercial trade, finance, and manufacturing, while the south developed an economy around plantation agriculture. This meant that northerners had a preference for Whiggish internal improvements over land-grabbing expansion. But this had its own problems and contradictions- the northern oligarchy made a lot of money from the southern political economy, and had an interest in keeping the two of them enmeshed together, which is basically why they kept bending over backwards to appease the increasingly-unappeasable Planter class. Although, as craven as the Yankee oligarchs were, they were ultimately a lot smarter than the Planters when it came to seeing the big picture of their class interests. Anyway, that's basically why abolitionism arose in the northeast first.