In foreign policy, Eisenhower put in place what became known as "brinkmanship," or the policy of taking the nation to the brink of all-out war in confronting the Soviet Union. He relied on the threat of massive retaliation with Hydrogen and Atomic Bombs to deter communist aggression. This buildup required the development of a large stockpile of nuclear weapons including IRBMs (Intermediate Range Ballistic Missiles) and ICBMs (Intercontinental Ballistic Missiles). Eisenhower’s heavy reliance on nuclear deterrence, however, prompted some critics to charge that the United States lacked the flexibility to fight small, non-nuclear wars around the periphery of the Soviet-Chinese bloc. They also argued that it was irresponsible to threaten, in effect, the end of the world if the Soviet Union were to engage in any hostile act.