<P> These pillars are interrelated and mutually reinforcing . An effective nonproliferation regime whose members comply with their obligations provides an essential foundation for progress on disarmament and makes possible greater cooperation on the peaceful use of nuclear energy . With the right to access the benefits of peaceful nuclear technology comes the responsibility of nonproliferation . Progress on disarmament reinforces efforts to strengthen the nonproliferation regime and to enforce compliance with obligations, thereby also facilitating peaceful nuclear cooperation . The "pillars" concept has been questioned by some who believe that the NPT is, as its name suggests, principally about nonproliferation, and who worry that "three pillars" language misleadingly implies that the three elements have equivalent importance . </P> <P> Under Article I of the NPT, nuclear - weapon states pledge not to transfer nuclear weapons or other nuclear explosive devices to any recipient or in any way assist, encourage or induce any non-nuclear - weapon state in the manufacture or acquisition of a nuclear weapon . Under Article II of the NPT, non-nuclear - weapon states pledge not to acquire or exercise control over nuclear weapons or other nuclear explosive devices and not to seek or receive assistance in the manufacture of such devices . Under Article III of the Treaty, non-nuclear - weapon states pledge to accept IAEA safeguards to verify that their nuclear activities serve only peaceful purposes . </P> <P> Five states are recognized by NPT as nuclear weapon states (NWS): China (signed 1992), France (1992), the Soviet Union (1968; obligations and rights now assumed by the Russian Federation), the United Kingdom (1968), and the United States (1968). These five nations are also the five permanent members of the United Nations Security Council . </P> <P> These five NWS agree not to transfer "nuclear weapons or other nuclear explosive devices" and "not in any way to assist, encourage, or induce" a non-nuclear weapon state (NNWS) to acquire nuclear weapons (Article I). NNWS parties to the NPT agree not to "receive", "manufacture", or "acquire" nuclear weapons or to "seek or receive any assistance in the manufacture of nuclear weapons" (Article II). NNWS parties also agree to accept safeguards by the International Atomic Energy Agency (IAEA) to verify that they are not diverting nuclear energy from peaceful uses to nuclear weapons or other nuclear explosive devices (Article III). </P>

When did the us sign the nuclear non-proliferation treaty