Secret service History 141 World War, 1939-1945 103 Spies 62 Intelligence service 47 Military intelligence 21 World War, 1914-1918 20 more ... Espionage 17 Politics and government 16 Underground movements 15 Campaigns 12 Foreign relations 12 Vietnam War, 1961-1975 12 Cold War 11 Espionage, German 11 Cryptography 8 Intelligence officers 8 Internal security 8 Police 8 War 8 Espionage, British 7 Women spies 7 Holocaust, Jewish (1939-1945) 6 Anti-Nazi movement 5 International relations 5 Military campaigns 5 Officials and employees 5 Terrorism 5 Aerial operations, American 4 Diplomatic relations 4 less ...