Americans' eagerness to expand westward caused a long series of Indian Wars and an Indian removal policy that stripped the native peoples of their land. The Louisiana Purchase of French-claimed land under President Thomas Jefferson in 1803 almost doubled the nation's size. The War of 1812, declared against Britain over different complaints and fought to a draw, strengthened U.S. nationalism. A series of U.S. military invasions into Florida led Spain to give up it and other Gulf Coast territory in 1819. The United States took over the Republic of Texas in 1845. The idea of Manifest destiny became popular during this time. The 1846 Oregon Treaty with Britain led to U.S. control of the present-day American Northwest. The U.S. victory in the Mexican–American War resulted in the 1848 cession of California and much of the present-day American Southwest. The California Gold Rush of 1848–49 further encouraged western relocation. New railways made relocation easier for settlers and increased conflicts with Native Americans. Over a half-century, up to 40 million American bison, or buffalo, were murdered for skins and meat and to ease the railways' spread. The loss of the buffalo, which were valuable to the plains Indians, caused many native cultures to become gone forever.