Secret service History 49 World War, 1939-1945 49 Spies 22 Intelligence service 19 World War, 1914-1918 14 Politics and government 9 more ... Vietnam War, 1961-1975 8 Cryptography 7 Military intelligence 6 Underground movements 6 Foreign relations 5 Holocaust, Jewish (1939-1945) 5 International relations 5 Espionage 4 War 4 Women spies 4 Campaigns 3 Electronic intelligence 3 Participation, Female 3 War criminals 3 Anti-Nazi movement 2 Arab-Israeli conflict 2 Censorship 2 Cold War 2 Collaborationists 2 Espionage, Soviet 2 Intelligence officers 2 Kidnapping, 1944 2 Manners and customs 2 less ...