During the years after the Cuban missile crisis, both superpowers treaded more warily to avoid direct confrontations, but traditional Cold War concerns kept them expanding their nuclear arsenals and preparing for the possibility of World War III. Motivated by fear and suspicion, but also by diplomatic and political purposes, both Moscow and Washington invested huge sums in thousands of nuclear weapons and intercontinental delivery systems. During the 1960s, the United States deployed over a thousand intercontinental ballistic missiles (ICBM), hundreds of submarine-launched ballistic missiles (SLBMs), and took the arms race in a new qualitative direction by developing accurate multiple independently targetable re-entry vehicles (MIRVs). The Soviets, determined never to be outmatched again in a crisis, began to field a formidable ICBM force. Before Moscow reached strategic parity with Washington, and ended US nuclear supremacy, however, a stalemate had emerged, where neither side could launch a preemptive strike to gain a military advantage without incurring horrific losses. While the leaders of the superpowers recognized that nuclear weapons were militarily unusable, except in the most extreme circumstances, they nevertheless wanted them for deterrence and for diplomatic leverage.
In Europe, the cockpit of Cold War rivalries, apprehensions about military force imbalances and fears of nuclear blackmail and first strikes gave nuclear weapons a central role in alliance policies and politics. To validate security guarantees and to deter political and military threats, both the Soviet Union and the United States stockpiled thousands of tactical nuclear weapons on European soil.