The effort to constrain the acquisition and use of nuclear weapons is perhaps the most ambitious attempt ever made to extend the civilizing reach of the rule of law over humankind’s destructive capacity. The United States, the Soviet Union, and other states laid the foundation for this mission in the 1960s with the negotiation of the nuclear Non-Proliferation Treaty (NPT).

The treaty enshrines three basic bargains at the core of the nonproliferation regime. States that had not tested nuclear weapons before January 1, 1967, promised not to seek the transfer or manufacture of nuclear weapons, while the states that had already tested nuclear weapons promised to work seriously toward eliminating their nuclear arsenals. States with advanced nuclear capability promised to assist non-nuclear weapon states to develop “the applications of nuclear energy for peaceful purposes.” And, less formally, states with nuclear weapons (primarily the United States and the Soviet Union) pledged to come to the assistance of non-nuclear-weapon states if they were threatened with nuclear attack.