As the nation expanded westward, the dispute over slavery intensified. Citizens of Southern slave states clashed with Northern activists who were morally opposed to slavery. Former president Thomas Jefferson, in his late seventies at the time of the Missouri Compromise, once described the difficult situation slavery presented.
Justice is in one scale, and self-preservation in the other.
Missouri's ratification would inevitably upset the tenuous balance between slave and free states in the U.S. Senate. Supported by Senators Stephen A. Douglas of Illinois and Daniel Webster of Massachusetts, Henry Clay again suggested a compromise. The compromise, while not wholly satisfactory to either the North or the South, temporarily preserved the Union. Because most of the Western territories lay north of the dividing line legislated by the Missouri Compromise, they were already off limits to slavery. Southern representatives acted to preserve their predominance in the Senate by stalemating applications that would grant the territories statehood.