The event that occurred first: The Missouri Compromise
- The Missouri Compromise was passed in Congress in 1820. It admitted Missouri into the Union as a slave state with Maine being added as a free state at the same time, to keep the balance of slave and free states equal. It also prohibited any future slave states north of the latitude line 36 1/2 degrees north of the equator in territories of the Louisiana Purchase, with the exception of Missouri (north of that line) being admitted as a slave state.
The other items:
- Discovery of gold in California was in 1848.
- Application for statehood by California was in 1849.
- The Compromise of 1850 was (obviously) in 1850. As part of the Compromise of 1850, California was admitted to the Union as a non-slavery state.