1). Through the Louisiana Purchase of 1803 and treaties with Spain and Britain, the nation's borders moved west to the Rocky Mountains, north to the 49th parallel, and south to Florida and the Gulf of Mexico.2).With the Adams-Onis Treaty of 1819, Spain settled a long dispute with the United States over its southern border.3). In 1836, U.S. annexed Texas and in 1847, Texas became a state of U.S.4). In 1846, U.S. and Great Britain reached Oregon Treaty to divide the territory at the 49th parallel.5). After the Mexican-American War, in 1848, the Treaty of Guadalupe was signed, establishing the Rio Grande and not the Nueces River as the U.S.-Mexican border. Under the treaty, Mexico also recognized the U.S. annexation of Texas, and agreed to sell California and the rest of its territory north of the Rio Grande for $15 million plus the assumption of certain damages claims.6). In 1853, U.S. bought a small strip of land along the U.S.-Mexico border for $10 million. The Gadsden Purchase included land in present-day Arizona and New Mexico.7). In 1867, U.S. purchased Alaska for the cost of $7.2 million — about two cents per acre from Russia.