Why did abolitionists from the North care if new territories entered the Union as free states or slave states?

Voting power

Explanation:

Abolitionists sought to abolish slavery in the United States and for that to happen they needed a majority in Congress. New States also got to send representatives to Congress and vote on government policy.

It was therefore imperative that a state entered the Union as a free state so that when it sent representatives to Congress (especially the Senate), those reps could vote in favor of abolishing or at least limiting slavery.

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