The development of military arms harnessing nuclear energy for mass destruction has inspired continual efforts to control them. Since 1945, the United States, the Soviet Union, the United Kingdom, France, the People’s Republic of China (PRC), Israel, India, Pakistan, North Korea, and South Africa acquired control over these powerful weapons, though Pretoria dismantled its small cache in 1989 and Russia inherited the Soviet arsenal in 1996. Throughout this period, Washington sought to limit its nuclear forces in tandem with those of Moscow, prevent new states from fielding them, discourage their military use, and even permit their eventual abolition. Scholars disagree about what explains the United States’ distinct approach to nuclear arms control. The history of U.S. nuclear policy treats intellectual theories and cultural attitudes alongside technical advances and strategic implications. The central debate is one of structure versus agency: whether the weapons’ sheer power, or historical actors’ attitudes toward that power, drove nuclear arms control. Among those who emphasize political responsibility, there are two further disagreements: (1) the relative influence of domestic protest, culture, and politics; and (2) whether U.S. nuclear arms control aimed first at securing the peace by regulating global nuclear forces or at bolstering American influence in the world. The intensity of nuclear arms control efforts tended to rise or fall with the likelihood of nuclear war. Harry Truman’s faith in the country’s monopoly on nuclear weapons caused him to sabotage early initiatives, while Dwight Eisenhower’s belief in nuclear deterrence led in a similar direction. Fears of a U.S.-Soviet thermonuclear exchange mounted in the late 1950s, stoked by atmospheric nuclear testing and widespread radioactive fallout, which stirred protest movements and diplomatic initiatives. The spread of nuclear weapons to new states motivated U.S. presidents (John Kennedy in the vanguard) to mount a concerted campaign against “proliferation,” climaxing with the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Richard Nixon was exceptional. His reasons for signing the Strategic Arms Limitation Treaty (SALT I) and Anti-Ballistic Missile Treaty (ABM) with Moscow in 1972 were strategic: to buttress the country’s geopolitical position as U.S. armed forces withdrew from Southeast Asia. The rise of protest movements and Soviet economic difficulties after Ronald Reagan entered the Oval Office brought about two more landmark U.S.-Soviet accords—the 1987 Intermediate Ballistic Missile Treaty (INF) and the 1991 Strategic Arms Reduction Treaty (START)—the first occasions on which the superpowers eliminated nuclear weapons through treaty. The country’s attention swung to proliferation after the Soviet collapse in December 1991, as failed states, regional disputes, and non-state actors grew more prominent. Although controversies over Iraq, North Korea, and Iran’s nuclear programs have since erupted, Washington and Moscow continued to reduce their arsenals and refine their nuclear doctrines even as President Barack Obama proclaimed his support for a nuclear-free world.