• 63 History
• 11 Frontier and pioneer life
• 10 Study and teaching
• 9 World War, 1939-1945
• 8 Civil engineering
• 8 Politics and government
• 6 Hydrology
• 6 Outlaws
• 6 Water
• 5 Extinction (Biology)
• 5 Indians of North America
• 5 Mass extinctions
• 4 Depressions
• 4 Economic conditions
• 4 Imperialism
• 4 Industrialization
• 4 Technological innovations
• 4 Wars
• 3 Architecture, American
• 3 Biography
• 3 Commerce
• 3 Defense industries
• 3 Emigration and immigration
• 3 Entrepreneurship
• 3 Gold mines and mining

• 151 Films Media Group
• 44 Infobase

• 151 English

• 38 United States
• 11 West (U.S.)
• 6 Europe
• 3 Canada
• 3 China
• 2 Alaska
• 2 Great Plains
• 2 Japan
• 2 Oklahoma
• 2 Texas
• 1 Afghanistan
• 1 Africa, North
• 1 Appomattox County (Va.)
• 1 Aswān (Egypt)
• 1 Baṣrah (Iraq)
• 1 Boston (Mass.)
• 1 Cambodia
• 1 Chicago (Ill.)
• 1 Dawson (Yukon)
• 1 Deadwood (S.D.)
• 1 England
• 1 Germany
• 1 Grand Coulee Dam (Wash.)
• 1 Great Wall of China (China)
• 1 Iraq

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