Complex sentence: In the 1770s, blacks throughout New England began sending petitions to northern legislatures demanding freedom; by 1800, all of the northern states had abolished slavery or set measures in place to gradually reduce it.
Split into simpler sentences: In the 1770s, blacks throughout New England began sending petitions to northern legislatures demanding freedom. By 1800, all of the northern states had abolished slavery or set measures in place to gradually reduce it.