The Mexican-American War, and the acquisition by the USAof extensive new territories in the West.
Republican party
The Missouri Compromise was put into place in 1820 in the US Congress. It was put into place to create balance between slave owning and non slave owning states in the US a that time.
The Missouri Compromise was put forth by Senator Henry Clay in an attempt to prevent the addition of the new territory of Missouri, as a slave slate, from tipping the balance of power in Congress to Southern States. Since Missouri was not an official state until this compromise's passing, the state's people had no representation in Congress or ability to affect this bill.
The 1820 Missouri Compromise was put in place by Congress in order to maintain the balance between slave States and non slave States. Senator Henry Clay was one of the key politicians in formulated the Compromise.
The 1820 Missouri Compromise was put in place by Congress in order to maintain the balance between slave States and non slave States. Senator Henry Clay was one of the key politicians in formulated the Compromise.
Henry Clay
Senator Stephen A. Douglas put forth the argument that if the Missouri Compromise of 1850 really was a compromise, it had to put forward a consistent principle. If it did not then it was not a compromise, but instead a modus vivendi arrangement. The main problem of this characterization is that Douglas was asking a rhetorical question. Douglas was the one to know inasmuch as he helped put it together.
Henry clay put it together
The Missouri compromise made Missouri a slave state and so naturally put it into the Confederate camp when the Civil War broke out. Free state Illinois is just across the Mississippi River from St. Louis so there many ties with the Union as well.
Douglas wanted to abandon the Missouri Compromise because he wanted to put in place his own Kansas- Nebraska Act. This act would expand railroads and allow territories to choose for themselves if they wanted to be free or slave states.
The crisis over Missouri Compromise exposed the divisions of the country on the contentious issue of slavery. The line that literally divided the territories that would become states put the Union into a precarious balance that could easily tip in favor of the slave states.
The vast new territories ceded from Mexico invalidated the Missouri Compromise that had kept the peace for thirty years. So a new compromise had to be worked out, and this one did not last.