Historical Timeline
 1820 The Missouri statehood controversy became a national issue as the issue of slavery was debated.  The "Missouri Compromise" allowed Missouri to enter the Union as a slave state and Maine to enter as a free state, thus keeping the balance of slave and free states equal in Congress.  Although Missouri was allowed to enter as a slave state, the remaining portion of the Louisiana Purchase area north of the 36  30' line was to be forever free of slavery.  
 1820 Maine is admitted to the Union as a free state.