Which legislative agreement allowed Missouri to enter as a slave state and Maine as a free state?

The Missouri Compromise is the correct answer because it was specifically designed to address the contentious issue of slavery’s expansion into new territories and states. Enacted in 1820, this legislative agreement allowed Missouri to enter the Union as a slave state while simultaneously admitting Maine as a free state. This was a crucial attempt to maintain the balance of power between slave and free states in Congress.

Additionally, the Missouri Compromise established the 36°30' parallel as a boundary line in the Louisiana Purchase territory, north of which slavery was prohibited (except in Missouri), further illustrating its significance in the ongoing debates about slavery in the United States. This compromise was a pivotal moment in the early 19th century as it reflected the deep divisions in American society regarding the institution of slavery and its implications for new states entering the Union.