During the Khrushchev reign, the tension between the United States and the Soviet Union was at an all time high. A perfect example of this would be the Cuban Missile Crisis. Khruschev's decision to put Soviet missiles into Cuba (which is only 90 miles from the United States) was one factor that almost lead to all out nuclear warfare between these two countries.
Brezhnev's regime was one eased tensions between the US and Soviet Union. Brezhnev and President Richard Nixon reduced tensions between the US and Soviet Union through a series of treaties based on reducing the amount of arms (weapons) each country was developing.