History World War, 1939-1945 114 Politics and government 64 Campaigns 45 Encyclopedias 35 Pictorial works 35 Airplanes, Military 32 Biography 32 Military art and science 31 Armed Forces 25 Foreign relations 25 Dictionaries 19 Islam 17 Equipment and supplies 16 Warships 16 20th century 14 Airplanes 14 Sources 14 World War, 1914-1918 14 Aerial operations, British 13 History, Military 13 Naval operations 13 Terrorism 13 United States 13 Civil War, 1861-1865 12 Communism 12 Juvenile literature 12 Vietnamese Conflict, 1961-1975 12 Civilization 11 Military history, Modern 11