World War, 1914-1918 53 History 28 Campaigns 9 Juvenile literature 8 World War, 1939-1945 8 Aerial operations 7 Pictorial works 6 Airplanes, Military 4 Biography 4 Tanks (Military science) 4 Air warfare 3 Causes 3 Naval art and science 3 Naval history, Modern 3 Naval operations 3 Sources 3 World War 3 1939-1945 2 Aerial operation 2 Aerial operations, American 2 Air pilots 2 Armored vehicles, Military 2 Chemical warfare 2 Diplomatic history 2 Encyclopedias 2 Foreign relations 2 Germany 2 Great Britain 2 History, Modern 2 Military uniforms 2