The Missouri Compromise split the Louisiana Territory with the North being free from slavery and the South being allowed to have slavery.
The issue of slavery was a rising concern and with each state entering into the Union the balance of slave and free states was skewing. With a new land mass to be concerned with, the government needed a compromise to deal with new states coming into the Union in an effort to maintain slave v. free states. Missouri was entered as a slave state and Maine entered as a free state. The compromise also set the 36'30 line splitting Louisiana Territory. The compromise would last until 1850.
The Missouri Compromise established that territory from the Louisiana Purchase above 36°30' would be free from slavery. The Missouri Compromise went into effect on February 17, 1819.