At the dawn of the Cold War, American policy makers relied confidently on the nuclear monopoly enjoyed by the United States as a trump card in the Soviet-American diplomatic and political contest of the postwar era. Once the Soviet Union developed its own nuclear arsenal after 1949, however, public anxiety in the United States increased as the possibility of thermonuclear war took on frightening dimensions during the Eisenhower years. Placing its eggs in the nuclear basket, the Eisenhower administration relied on a large arsenal and deterrence theory in its determined effort to counter Soviet advances in an escalating arms race. The idea of deterrence was based on the assumption that a huge nuclear stockpile would discourage any adversary from launching a first strike in view of the overwhelming response (massive retaliation) the United States was capable of delivering.