History 309 World War, 1939-1945 250 Aerial operations 155 Foreign relations 153 Politics and government 137 United States 91 Aerial operations, American 84 Biography 80 Aerial operations, British 67 Campaigns 52 Terrorism 47 Airplanes, Military 38 Social conditions 38 Economic conditions 31 Juvenile literature 30 Therapeutic use 30 Military policy 29 Armed Forces 26 World War, 1914-1918 25 Fighter pilots 23 Islam 23 World politics 23 Relations 22 World war, 1939-1945 22 Herbs 21 Prevention 20 National security 19 Personal narratives, American 19 Vietnam War, 1961-1975 19 Air warfare 17