The Cold War between the U.S. and U.S.S.R. prompted negotiations to lower the risk of nuclear war. The 1972 Anti-Ballistic Missile (ABM) Treaty reinforced the idea of nuclear deterrence through mutually assured destruction: without missile defense, destruction was more likely. Everyone also agreed, having fewer missiles around was a good idea.

In 1973, the United Kingdom (UK) and Ireland joined the European Economic Community (EEC; predecessor to the European Union, EU) to address difficult economic issues. Common depressed economies and perceived inequalities between communities precipitated open violence in Northern Ireland, a UK nation sharing a 310-mile border with Ireland.

Seven countries, including Iran, agreed in 2015 to the Joint Comprehensive Plan of Action (JCPOA), constraining Iran’s ability to develop nuclear weapons. After signing, the U.S. Congress did not enact a resolution of disapproval for the JCPOA by their own self-imposed deadline. Without this disapproval, the JCPOA came into force under United Nations Security Council resolution 2231. Yet, in 2018, a new U.S. administration unilaterally withdrew from the JCPOA.