Why did the United States and Soviet Union build large nuclear arsenals during the Cold War?

During the Cold War, the United States and the Soviet Union built massive nuclear arsenals primarily to establish a deterrent effect against one another. The core objective was to ensure that any nuclear aggression by one superpower would be met with an overwhelming second strike, leading to the mutual annihilation of both nations—a doctrine that became known as mutual assured destruction (MAD).123

By maintaining large, diverse stockpiles—often organized into a nuclear triad of bombers, land-based missiles, and submarines—each side sought to guarantee that its retaliatory capability could survive a preemptive attack. This strategic competition was driven by:1

• Perceived Security: Both nations believed that possessing a superior or at least equivalent nuclear force was essential to prevent the other from gaining a decisive military advantage.13
• Strategic Parity: Policymakers, such as those under the John F. Kennedy administration, aimed to maintain a balance of power where neither side could win a nuclear conflict, thereby discouraging the initiation of war.1
• Arms Race Dynamics: Despite efforts to limit weapons through agreements like SALT, the intense ideological rivalry often led to continued expansion, as each side feared the other might achieve a technological or numerical breakthrough.13

Ultimately, these arsenals were built on the grim logic that the certainty of total destruction was the most effective way to prevent a global nuclear holocaust.14