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,

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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.