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I think the answer is D. Capital
This question is incomplete.
You forgot to include the series of events. Without those events, we do not have the proper references to answer the question.
However, trying to help you, we can comment on the following.
You are probably referring to the permanent conflicts and confrontations between the United States and the Soviet Union during the Cold War years. If that is the case, these events bring the world close to nuclear war "by creating a confrontation between the world's two superpowers."
Soviet leader Joseph Stalin kept control over occupied countries and instilled Communism. We are talking about East Germany, Romania, Albania, Hungary, Poland, and Czechoslovakia. The USSR supported the spread of Communism all over the world and the United States applied the policy of containment, trying to stop the spread of that political and economic ideology.
Both countries supported their respective sides in the Korean War and the Vietnam War. They also competed in the arms race and years later, in the space race.
These issues created too much tension and the world was on the brink of another war in the times of the Cuban missile crisis.
The answer is White House Staff
The biggest cause was disease spread from the people exploring.
