The United States fought Indian Wars west of the Mississippi River from 1810 to at least 1890. Most of these conflicts ended with the cession of Native American territory and their confinement to Indian reservations. Additionally, the Trail of Tears in the 1830s exemplified the Indian removal policy that forcibly resettled Indians. This further expanded acreage under mechanical cultivation, increasing surpluses for international markets. Mainland expansion also included the purchase of Alaska from Russia in 1867. In 1893, pro-American elements in Hawaii overthrew the Hawaiian monarchy and formed the Republic of Hawaii, which the U.S. annexed in 1898. Puerto Rico, Guam, and the Philippines were ceded by Spain in the same year, following the Spanish–American War. American Samoa was acquired by the United States in 1900 after the end of the Second Samoan Civil War. The U.S. Virgin Islands were purchased from Denmark in 1917.