Why was there a détente between the United States and Soviet Union in the 1970’s?

One of the key reasons as to why the United States sought détente, or an easing of relations, with the Soviet Union in the 1970’s was the internal domestic issues that arose out of the war in Vietnam. Since 1964, the United States had been conducting a large-scale military intervention in Vietnam, and by 1968, when the Nixon administration came to power, the war was not going well. It had cost tens of thousands of American lives and was deeply unpopular at home. Seeking to ease tensions on the European continent so it could focus resources on other areas such as the Middle East, the U.S, building on the Ostpolitik of German chancellor Willy Brandt, signed the Helsinki Accords in 1977. This agreement ensured that both the West and the Eastern bloc recognised the inviolability of the current borders in Europe, defusing concerns about the outbreak of war over a border dispute. Although there was a clause committing both sides to respect human rights, which was admittedly not closely followed, the Helsinki Accords were fundamental in reducing tensions between the superpower blocs, and allowing the U.S to recover from its intervention in Vietnam.As for the Soviet Union, it was well aware by the 1970’s that it was lagging behind the Western powers in economic strength and, as a result, technological development. In light of both these factors, an new nuclear arms race would not be desirable. Building on the Test Ban Treaty of 1963, the USSR and the U.S both signed the Nuclear Proliferation Treaty (NPT) in 1970 – which prevented nuclear proliferation – and the SALT Treaty in 1972, which reduced and froze the number of ballistic missiles each state could deploy. These attempts at arms reduction were vital in easing tensions between East and West, especially in Europe, and allowed the USSR to focus on domestic economic development without having to increase military spending, which by 1975 had reached over a quarter of total spending.