Republic occupying the central portion of North America, along with Alaska, Hawaii and a large number of island possessions in the Caribbean Sea and the Pacific Ocean. The United States was formed from the union of the 13 British mainland North American colonies south of Canada in 1783, after an eight-year war against Great Britain. During 1803-53, the United States expanded rapidly westward, increasing its territory through conquest, purchase and negotiation. Alaska was purchased from Russia in 1867, and in 1898, Hawaii was annexed, at the request of its inhabitants. In the following year, Puerto Rico, Guam and the Philippines were acquired from Spain, following the short Spanish-American War. The United States long avoided involvement in foreign affairs, except in the Western Hemisphere, where U.S. interest was concentrated.
In 1917, the United States entered World War I and played an instrumental role in the defeat of the Central Powers. Following the war, it reverted to its normal isolationalist policy. During the first two years of World War II, the United States resisted involvement, although its sympathies were strongly with the Allies, to whom it supplied economic aid. The Japanese attack on the major U.S. Pacific naval base at Pearl Harbor forced the country into the war. Again, the United States played the decisive part in defeating Germany and its allies.
Following World War II, the United
States realized that it could not avoid international problems by
ignoring them and embarked on a policy of active involvement in the
regions where its interests were paramount. U.S. economic aid sparked
the European postwar economic boom, and its administration of Japan saw
the rapid expansion of Japanese industry. U.S. stamps were first issued
in 1847, although a number of local postmasters had been issuing
provisional stamps since 1845. U.S. issues have been used in many
nations throughout the world, reflecting, in most cases, the presence of
American troops. Most U.S. possessions use regular U.S. stamps.