What led to a period of an improved relationship between the United States and the Soviet Union in the early 1970s?

The improved relationship was part of a period known as détente, when the United States and Soviet Union took steps to reduce tensions. In 1972, they signed an agreement to prevent dangerous incidents between their military forces, including at sea. They did not agree to eliminate all nuclear weapons or to support the spread of communism, so D is correct.

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