Answer:
Cold War
Step-by-step explanation:
The "Cold War" started in 1945 after the World War II and it lasted for many years. The tension was between the U.S.A. and the Soviet Union. Even before it started, both countries have already been wary of each other. The U.S.A. didn't like the idea of "communism" under Joseph Stalin, Russia's leader, while the Soviet resented America's delayed entry into World War I. Such situation increased their indifferences.
Later on, both countries raced to make the deadliest atomic bomb in the world. Atomic bomb testing were conducted which increased the nuclear threats between both countries. People feared for their lives and began having drills in case of a nuclear attack.