In late 1849, California sought admittance into the Union as a free state.
The ratio of slave to free states at the time was even - 15:15. No territory applied for statehood at the same time as California, however, so imbalance became inevitable.
Sectionalist controversy raged. Northerners campaigned to outlaw slavery in all Western territories, inspiring talk of secession in the South.
To prevent further escalation of the North-South conflict, moderates and unionists, headed by Henry Clay, framed the Compromise of 1850.
The Compromise of 1850 admitted California as a free state, banned the slave trade in Washing D.C., and lent Mexican-ceded territories popular sovereignty - territories' residents could vote to determine their slavery policy.
The Compromise of 1850 also established a new Fugitive Slave Law, which was meant to appease the pro-slavery South. All Americans were required by law to cooperate in returning runaway slaves to their masters. The Law also gave rise to kidnappings of free blacks.