Relations after World War II between the United States and the Soviet Union deteriorated into cold war because the two nations had radically different ideas of how the post-war world should be configured. For instance, while the USSR had agreed to allow democratic elections in the Eastern European countries it had liberated from Nazi rule, in reality, Stalin had no intention of allowing that to happen. From his point of view, which in fact was true, the Russians had carried the brunt of the death and pain in the European war while the US and Great Britain dragged their feet on invading Europe and drawing off German fire from the Soviets. Stalin was utterly determined to have a loyal set of buffer states (what we might call puppet states) between his country and Germany. For him, keeping Soviets safe from another attack from the west was of paramount importance.
However, from the point of the view of the US, which was also not wrong, Stalin betrayed his agreement and committed a backstab by ramming communist governments down the throats of his satellites states. The US took this as an aggressive act meant to spread communism worldwide. In fact, this was true, as Stalin did want to spread communism as far he could, while the US wanted to spread democratic capitalism. This situation led to a volatile situation in many parts of the world, particularly in southeast Asia and Africa, where proxy wars were fought to block and/or advance communism.
Neither country communicated well with the other, but fundamentally, each superpower was committed to a worldview that was antagonistic to and distrustful of the other.