The UN has been credited with negotiating many peaceful settlements, mediating regional conflicts and preventing WWIII. Though the primary responsibility to do so is of the Security Council, the 'Uniting for Peace Resolution' was adopted in November of 1950, allowing the General Assembly to also make recommendations for united actions of the members. Regional military alliances like NATO and the Warsaw Treaty Organization, etc. were established by Article 51 of the Charter in case the Security Council was unable to carry out its role as a peacekeeper.

The Suez Crisis in 1956, Congo in 1960, Cyprus in 1964, the Middle East crisis in 1974 and the Lebanon crisis in 1978 are good examples of the times when the UN dispatched forces for peacekeeping. In 1993 UN Peace Keeping Forces(PKF) were stationed in 13 nations (Cambodia, Yugoslavia, Somalia, Mozambique, Angola, etc.). They stayed in Croatia, Yugoslavia and Sierra Leone until 1999. The PKF was awarded the Nobel Peace Prize in 1988.

A Korean 'Sangrocksu Unit' of 419 people consisting of 1 battalion of special forces, medical personnel and engineers was dispatched to East Timor, Indonesia in October 1999, to contribute to UN peacekeeping.

The UN passed a resolution to limit weapons of mass destruction, including atomic bombs, to reduce spending on arms and the number of military personnel in 1946. The Atomic Energy Commission and the Commission for Conventional Armaments were merged to create the Disarmament Commission in 1952, and the UN established its relations with IAEA to achieve peaceful use of atomic energy in 1957.

Using nuclear weapons was declared a criminal act against International Law, the Charter and Humanity in 1961. Nuclear weapons testing was banned in 1963 and a partial Nuclear Nonproliferation Treaty was signed in 1968. The treaty on the prohibition on emplacing seabed nuclear weapons came into force in 1971.

The UN in its continuing efforts banned chemical and biological weapons in 1972, passed a resolution to prohibit hostile use of environmental modification techniques in 1976 and banned certain conventional weapons of destruction in 1980. Additionally, the UN played active roles in effecting SALT between the USA and USSR in 1972 and 1979 and START in 1991 and 1993.

The Security Council established an interim international administration following the end of NATO air bombing and the withdrawal of Yugoslav forces from Kosovo. At the Disarmament Conference in Tokyo Japan, in 1999, issues on nuclear disarmament, nuclear nonproliferation, disarmament of conventional weapons and peace in the Far East, etc. were discussed.