How did improved relations affect the United States and the Soviet Union?
I assume that you are asking about the improved relations between the two countries, known as "detente," that existed for most of the time between 1972 and 1980. If so, I would argue that the improved relations did not really have that much of an impact at all. As the link below says,
Ultimately, détente was not an alternative to the Cold War but a less belligerent way to wage it. A competitive relationship still existed between the United States and the Soviet Union.
Detente did bring about at least two very important steps. The first was the opening of diplomatic relations between the US and China. The second was the SALT I treaty that, to a degree, limited the nuclear weapons arsenals of the two countries.
However, neither of these events really changed the US or the Soviet Union, at least not in any clear-cut ways. Neither of them stopped the US and the Soviet Union (or China, for that matter) from distrusting one another. SALT did not stop the arms race either. By 1980, with the election of Ronald Reagan, detente was over.
I would argue, then, that there was very little lasting impact on the US or the Soviet Union. Instead, detente was simply a lull in the Cold War.