Nuclear weapons certainly have NOT prevented wars between nuclear weapons states and non-nuclear weapons states. (Ask any Vietnam or Gulf War veteran!) Nuclear weapons states have been involved in more wars than non-nuclear weapons states. Between 1945 and 1997, nuclear weapons states have fought in an average of 5.2 wars, while non-nuclear weapons states averaged about 0.67 wars.
Some advocates of nuclear weapons continue to claim that such weapons have at least prevented a large-scale conflict between major powers (specifically between the U.S. and the former USSR). Though there have not been any world wars since the development and use of nuclear weapons, this is not proof that nuclear weapons have been responsible for keeping the peace. It is unclear that any of the major powers wanted to fight on a large scale with each other.
According to the Canberra Commission, the idea that the former Soviet Union was plotting to invade Europe is open to question in light of recent investigations made possible due to the end of the Cold War. The horrific experiences of World War II, in which some 40 to 50 million people died, had convinced leaders in both the East and the West that another world war should be avoided at almost any price.
Some even claim that the presence of nuclear weapons in war-prone regions such as India and Pakistan has introduced caution and served as a stabilizing force. Others suggest, however, that Pakistan’s acquisition of a nuclear capability has hardened its resolve not to settle the Kashmir crisis and allowed it to feel safe behind a “nuclear shield” as it supports Kashmiri militancy.
If the only use of nuclear weapons is to deter enemy use of nuclear weapons, then the best way to end the threat of nuclear war is to eliminate these weapons altogether.”
Henry Kissinger “Since deterrence can only be tested negatively, by events that do not take place, and since it is never possible to demonstrate why something has not occurred, it became especially difficult to assess whether the existing policy was the best possible policy or just.”