National security -- Security measures Terrorism -- 4 Prevention 3 Merchant marine -- 2 Military policy 2 Air power -- 1 more ... Civil defense 1 Civil defense -- 1 Defenses 1 Harbors -- 1 Homeland security 1 Information warfare -- 1 Infrastructure -- 1 National security 1 Politics and government -- 1 Prevention. -- 1 Safety measures 1 Security Management 1 Security measures -- 1 Transportation -- 1 United States 1 War on Terrorism, 2001-2009 1 War on terrorism, 2001- 1 less ...