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Missouri Compromise (1820)
Missouri entered as a slave state, Maine entered as a free state, no slavery allowed in unorganized territory about the 36'30' Latitude line. -
Compromise of 1850
Idea of popular sovereignty emerged. California entered as a free state, NM and Utah territory gets the choice to be free or not (popular sovereignty, stronger fugitive slave laws are passed to make the compromise "fair" for the south.