For a while after the Missouri Compromise in 1820 everything seemed to be working with the balance between free and slave states. There were fifteen free states and fifteen slave states. When California applied for statehood, the balance would be disturbed since it was a free state. Again, there was a lot of debate in Congress.
Henry Clay, the senator from Kentucky who worked out the Missouri Compromise, again had an idea for compromise. He suggested that California should be admitted to the Union and that the citizens of the New Mexico and Utah territories should decide whether they would be admitted as free or slave states. In exchange, he suggested that the northern states adopt the Fugitive Slave Law.
These suggestions were accepted and California was admitted as a free state. The balance was now sixteen free states and fifteen slave states, but the runaway slaves in the north faced greater consequences. The Southern states thought this was a good compromise. See Fugitive Slave Law.
The Compromise of 1850 probably postponed the war for many years, but the balance of power also provoked. See Kansas-Nebraska Act.