Why did the free states like the Missouri compromise?

In an effort to preserve the balance of power in Congress between slave and free states, the Missouri Compromise was passed in 1820 admitting Missouri as a slave state and Maine as a free state. ... In 1854, the Missouri Compromise was repealed by the Kansas-Nebraska Act.

The World War 1 created a huge demand of labors and created several other job opportunities, several Americans moved their locations to grab these opportunities, thus the World War 1 caused the great migration.

The great migration occurred between 1916 to 1970 when more than 6 millions of African American moved from rural area to the urban residence in search of new job and better living. The world War created a high demand of workers and the government was paying good amount for that, people from all over the northern part of the United States moved toward the urban area to get these opportunities.

The great migration was a very massive movement of millions of black moving from north to south and grabbing the jobs of the locals out there. It is also known as the great Black Migration or the great Northward Migration. It was the most rapid mass movement in the history of the United States.