rom 1800 to 1850 territorial expansion tore the United States apart. Territorial expansion itself was not a debated issue. Spurred by the concept of Manifest Destiny, almost everyone believed that America should extend from sea to shining sea and maybe even farther. But it was the issue of the expansion of slavery into the new territories that pitted the North against the South and split our nation apart.
The first real crisis over territorial expansion took place in 1819-1821 over the admission of the state of Missouri. The proposed state of Missouri was the first (beside Louisiana itself) to be carved out of the Louisiana Purchase. It lay out of the jurisdiction of the Northwest Ordinance, which prohibited slavery in the Northwest Territories, and had a long tradition of slavery. Therefore, in 1817 Missouri applied to the Union as a slave state. The extension of slavery so far north and the threat of further expansion of slavery into all new territories of the U.S. created havoc in Congress. In February 1819, Congressman James Tallmadge, from New York, proposed an amendment that would prohibit any new slaves to enter the state and provided that all slave children born after the date of admission would be set free at the age of twenty-five. Tallmadge's gradual emancipation proviso received almost unanimous opposition from Southern Congressmen. The amendment twice passed the North dominated House of Representatives, only to be turned down by the balanced Senate. In December 1819, Maine applied for statehood as a free state. In the end a compromise was reached where Maine would enter the Union as a free state, Missouri would enter the Union as a slave state without restrictions, but in the remaining Louisiana territory slavery would be prohibited north of 36o30' (the Mason-Dixon Line). This is now known as the Missouri Compromise. The Missouri Compromise is commonly thought of the beginning of American Sectionalism, although signs were visible long before 1819.