Answer:
Soviet Union supported government of Fidel Castro and gave them a nuclear missiles that were located on the island. As the United States discovered the missiles they made it clear that they will even start a war even necessary if the missiles are not to be removed. That is why United States blocked Cuba and a crisis that lasted 13 days commenced.
Step-by-step explanation:
Historians are arguing that the Cuban Missiles Crisis was the closest thing to an open war between Soviet Union and United States. Both sides were prepared to engage themselves in war, and world was at the edge of nuclear war. Still, at the end agreement was made and war was stopped before it started.