The westward movement of the American population occurred in intermittent flurries of settlement. The first began early in the nation's history, resulting in the statehood of Vermont, Kentucky, Tennessee, and Ohio, all of which were admitted to the Union between 1791 and 1803. With the Louisiana Purchase the US doubled in size, opening up new regions to exploration and settlement. Once the War of 1812 ended, expansion began in earnest. The government was eager to enlarge the Union, and, accordingly, six new states joined the Union between 1816 and 1821: Indiana, Mississippi, Illinois, Alabama, Maine, and Missouri.