The role of peace groups since the end of the Second World War can only be fully understood in the context of the main developments in world politics since 1945. The experience of the Second World War, and the lessons derived from it, have had an important impact on thinking about war and peace. Technological developments in weaponry, in particular the H bomb and the intercontinental missile, have transformed the nature of warfare between the great powers and so promoted widespread popular movements aiming to prevent a nuclear holocaust. However, the Cold War between the USA and USSR, which structured world politics for forty years, restricted the possibilities for peace action.