Prior to European exploration, Alaska was inhabited by Inuit in the far north, Aleuts across much of the southern coast, and Indians in the southeast. The Russians established a presence on Kodiak Island in 1784 and traded for furs.In 1867, the United States purchased Alaska from Russia for $7,200,000 in 1867. Until 1884, Congress didn't bother to provide any civil authority in Alaska, giving administration to various departments of the federal government. A degree of civil government was established in 1884, using Oregon laws as a basis, with new law making reserved to Congress.The Yukon Gold Rush brought thousands of miners to Alaska in 1897 and 1898. Later, Alaska's own gold rush took place around Nome and Fairbanks. With the playing out of gold mining, the population of Alaska actually decreased in 1920 from the previous census.World War II brought a great deal of military activity to Alaska. The Alaska Highway was built to connect the state overland with the continent's industrial heartland. The only part of the United States to be invaded by Japan was the Aleutian Islands. In 1959, Congress granted their wish and Alaska became the 49th state.The discovery of major oil fields on the North Slope led to another boom for the Alaska economy. In 1989, the tanker Exxon Valdez ran aground in Prince William Sound, spilling much of its cargo of petroleum and causing enormous environmental damage. A debate continues in Congress about opening portions of the Alaska National Wildlife Refuge to oil exploration.