United States policy of deterrence during the Cold War underwent significant variations. The early stages of the Cold War were generally characterized by ideology of containment, an aggressive stance on behalf of the United States especially regarding developing nationsunder their sphere of influence. This period was characterized by numerous proxy wars throughout most of the globe, particularly Africa, Asia, Central America, and South America. A notable such conflict was the Korean War. In contrast to general opinion, George F. Kennan, who is taken to be the founder of this ideology in his Long Telegram, asserted that his ideas had been misinterpreted and that he never advocated military intervention, merely economic support.
With the U.S. drawdown from Vietnam, the normalization of U.S. relations with China, and the Sino-Soviet Split, the policy of Containment was abandoned and a new policy of détente was established, whereby peaceful coexistence was sought between the United States and the Soviet Union. Although all factors listed above contributed to this shift, the most important factor was probably the rough parity achieved in stockpiling nuclear weapons with the clear capability of Mutual Assured Destruction (MAD). Therefore, the period of détente was characterized by a general reduction in the tension between the Soviet Union and the United States and a thawing of the Cold War, lasting from the late 1960s until the start of the 1980s. The doctrine of mutual nuclear deterrence characterized relations between the United States and the Soviet Union during this period, and present relations with Russia.
A third shift occurred with President Ronald Reagan’s arms build-up during the 1980s. Reagan attempted to justify this policy in part due to concerns of growing Soviet influence in Latin America and the new republic of Iran, established after the Iranian Revolution of 1979. Similar to the old policy of containment, the United States funded several proxy wars, including support for Saddam Hussein of Iraqduring the Iran–Iraq War, support for the mujahideen in Afghanistan, who were fighting for independence from the Soviet Union, and several anti-communist movements in Latin America such as the overthrow of the Sandinista government in Nicaragua. The funding of the Contras in Nicaragua led to the Iran-Contra Affair, while overt support led to a ruling from the International Court of Justice against the United States in Nicaragua v. United States.
While the army was dealing with the breakup of the Soviet Union and the spread of nuclear technology to other nations beyond the United States and Russia, the concept of deterrence took on a broader multinational dimension. The U.S. policy on post–Cold War deterrence was outlined in 1995 in a document called “Essentials of Post–Cold War Deterrence”. This document explains that while relations with Russia continue to follow the traditional characteristics of Mutual Nuclear Deterrence, due to both nations continuing MAD, U.S. policy of deterrence towards nations with minor nuclear capabilities should ensure through threats of immense retaliation (or even preemptive action) that they do not threaten the United States, its interests, or allies. The document explains that such threats must also be used to ensure that nations without nuclear technology refrain from developing nuclear weapons and that a universal ban precludes any nation from maintaining chemical or biological weapons. The current tensions with Iran and North Korea over their nuclear programs are due in part to the continuation of this policy of deterrence.
From Wikipedia: https://en.wikipedia.org/wiki/Deterrence_theory