Question

Why was there good reason to fear a war between the United States and the Soviet Union?

Answer 1

The United States was a world power that was working very hard to spread democracy to other countries. They also had nuclear weapons.
The Soviet Union was a world power that was working very hard to spread communism to other countries. They also had nuclear weapons.

The United States was anti-communist. The Soviet Union was anti-democracy.

There was a lot of tension between the two powers because of these differences. Both had the power to start a nuclear war. Rough times.