The Anti-Ballistic Missile (ABM) Treaty, signed in 1972 as part of the SALT I negotiations, was a cornerstone of arms control efforts during détente. It played a crucial role in limiting the development of missile defence systems, which were seen as destabilising the strategic balance of power. By agreeing to restrict ABM systems to two sites each, later reduced to one, both the US and the Soviet Union acknowledged the importance of maintaining a balance of terror, essentially a mutual assured destruction scenario, which was believed to prevent either side from initiating a nuclear strike. The treaty was significant because it was one of the first major arms control agreements during the Cold War, representing a mutual commitment to reducing the risk of nuclear war. Its importance was further underscored when, decades later, the US's withdrawal from the treaty in 2002 was viewed with concern by many as a potential step towards a new arms race.

The Soviet invasion of Afghanistan in 1979 significantly challenged the principles established by the Helsinki Accords, particularly those relating to respect for sovereign boundaries and non-interference in the internal affairs of other states. The invasion was seen as a clear violation of the Accords' commitment to territorial integrity and peaceful coexistence. It demonstrated the Soviet Union's willingness to use military force to maintain its influence in the region, undermining the trust and cooperative spirit fostered by détente. This aggressive move also highlighted the limitations of the Helsinki Accords, as they were non-binding and lacked mechanisms for enforcement. The invasion thus not only strained US-Soviet relations but also raised questions about the effectiveness of détente and the viability of agreements made during this period.

The election of Ronald Reagan as US President in 1980 marked a significant shift in the Cold War's trajectory, especially in relation to the Soviet Union. Reagan's hardline anti-communist stance and commitment to a strong military contrasted sharply with the détente policies of his predecessors. He advocated for increased defense spending and initiated the Strategic Defense Initiative (SDI), escalating the arms race. Reagan's rhetoric often took on an aggressive tone, exemplified by his labelling of the Soviet Union as the "Evil Empire." These policies and statements signalled a clear end to the era of détente and a return to a more confrontational approach. This shift contributed to a period of heightened tensions known as the Second Cold War, characterised by increased military build-up, proxy wars, and a renewed emphasis on ideological confrontation. Reagan's presidency was pivotal in defining the Cold War's final phase, leading up to the eventual dissolution of the Soviet Union.

The Apollo-Soyuz Test Project, conducted in July 1975, was a historic joint space mission between the United States and the Soviet Union. It symbolised the spirit of détente by demonstrating that cooperation was possible even amidst the intense rivalry of the Cold War. The mission involved the docking of an American Apollo spacecraft with a Soviet Soyuz capsule, marking the first international manned spaceflight. Its significance lay not only in its technical achievements but also in its diplomatic and symbolic value. It served as a powerful illustration of how former adversaries could collaborate on shared goals, fostering a sense of mutual respect and understanding. This event was particularly impactful as it occurred against the backdrop of a space race that had, for years, epitomised the competitive nature of US-Soviet relations. The project also paved the way for future cooperation in space exploration, setting a precedent for subsequent joint ventures such as the International Space Station.

The Helsinki Accords, signed in 1975, were primarily aimed at improving relations between the Eastern and Western blocs by establishing a set of guidelines for political, economic, and human rights standards. The Accords had three main 'baskets': security, cooperation, and human rights. The security aspect sought to solidify boundaries and reduce the risk of armed conflicts. Economic cooperation aimed at increasing trade and scientific collaboration, while the human rights section encouraged greater freedoms within the signatory states. In terms of US-Soviet relations, these Accords were significant as they represented a mutual acknowledgment of coexistence and cooperation. Although the Accords were non-binding, they served as a diplomatic tool that helped to ease tensions and foster a climate of détente. The agreement on human rights, in particular, provided the US with a platform to address human rights abuses in the Soviet Union, adding a new dimension to their interactions.