Ballistic missile defenses National security 39 Military policy 30 Strategic Defense Initiative 27 Defenses 24 Ballistic missiles 22 Air defenses 19 Antimissile missiles 18 Appropriations and expenditures 18 Armed Forces 18 Deterrence (Strategy) 11 Missile attack warning systems 10 Nuclear arms control 10 Nuclear weapons 10 Foreign relations 9 Government policy 9 Military Science 9 TECHNOLOGY & ENGINEERING 9 Finance 8 Space weapons 7 Costs 6 Astronautics, Military 5 Evaluation 5 Intercontinental ballistic missiles 5 Military relations 5 Nuclear nonproliferation 5 Nuclear warfare 5 POLITICAL SCIENCE 5 Procurement 5 Technological innovations 5