The Lisbon Protocol to the 1991 Strategic Arms Reduction Treaty was an agreement by representatives of Russia, Belarus, Ukraine, and Kazakhstan that all nuclear weapons of the former Soviet Union on the soil of those four states would be destroyed or transferred to the control of Russia. All four states agreed to join the Treaty on the Non-Proliferation of Nuclear Weapons, with Russia the successor to the Soviet Union as a nuclear state, and the other three states joining as non-nuclear states. The protocol was signed in Lisbon, Portugal, on May 23, 1992.