In the period between 1800 and 1850 America experienced a marked change in national unity. Territorial expansion had a large effect on national unity in this period. Territorial expansion boosted national unity between 1800 and 1823, but it degraded national unity between 1824 and 1850. The time period between 1819 and 1824 was the transitional period from unity to disunity, because national unity fluctuated in this time period.
Between 1800 and 1823 the Louisiana Purchase and the Treaty of 1818 boosted national unity. First, the Louisiana Purchase boosted unity because it helped spur the Era of Good Feelings and it displayed Western loyalty. The 1803 Louisiana Purchase helped spur the Era of Good Feelings because it marked the beginning of the downfall of the Federalists. The Federalists opposed expansion because they feared that new territories would drain off their New England population and compete with New England economically, which would decrease their potency in America. When the Louisiana Purchase was made in 1803, the Federalists suffered a huge defeat and were reduced to mere sectionalists. Now the Jeffersonian Democrats were clearly becoming America's dominant party in the early 1800's. Because of the Louisiana Purchase, Federalist extremists took drastic action. Aaron Burr, an extreme Federalist, devised schemes to secede New England and New York from America, but he failed. He then attempted to secede the trans-Mississippi West, and he failed again because he could not gather enough support in the West. His failure to gain support displayed Western loyalty to the federal government, a mark of the national unity in this period. The Federalists' declining power set the stage for the Era of Good Feelings, which began in 1816 when the Federalist party died out. In the Era of Good Feelings, nationalism was highly prevalent because one political party, the Jeffersonian Republicans, dominated the country.