In 1819 the territory of Missouri was on the verge of being accepted as a state. A bill for statehood was underway in congress when James Tallmadge proposed an amendment which would accept Missouri as a free state, and drive existing slavery to extinction within one generation. The amended bill quickly passed the northern dominated House of Representatives, however in the equal representation senate the bill failed to pass. This led to the so called "Missouri Compromise" in 1820. The Missouri Compromise primarily involved the regulation of slavery in the western territories of the United States. With the exception of Missouri, this law prohibited slavery in the Louisiana Territory north of the 36*30' parallel. However after the Mexican American war the balance created by the Missouri Compromise would be toppled, requiring a new compromise. The compromise of 1850 was created by Henry Clay to accommodate the addition of the new land added after America's victory in the war with Mexico. The compromise was created to keep both sides - the North and the South - at an equal place in the battle against and for slavery. The compromise stated that California would be admitted as a free state, slave trade would be prohibited in the capital. The south would get to expand slavery west into the New Mexico and Utah territories. Additionally Texas would stop contesting its boundary with New Mexico and receive 10 million dollars. The compromise managed to stay the divide that would lead to the Civil War.
The situation in 1837 shows the 36-30 parallel as well as the distribution of slave and free states. Also the graph shows how the number of free states was catching up to and now equaled the number of slave states. The trend towards free states would continue up until the civil war.
The above is an excerpt from the proposed Tallmadge amendment, which shows the northern commitment to ending slavery and preserving the continent for freedom.
The addition of new lands was a cause of the compromises, and the compromises were created to settle any potential conflict that could arise between the North and South. The main goal for the South was to keep slavery from being completely abolished, while the North wanted to do the opposite. This divide escalated into the Civil War, and arguably ended only during the Civil Rights movements of the 1960's.