What alerted the united states that communism in cuba had become dangerous?

The event that alerted the United States that communism in Cuba had become dangerous was the Cuban Missile Crisis of 1962.

Explanation:

The Missile Crisis in Cuba is the name given to the conflict between the United States, the Soviet Union and Cuba in October 1962, generated as a result of the discovery by the United States of Soviet bases of medium-range nuclear missiles in Cuban territory.

It was one of the biggest crisis, together with the Berlin Blockade and the Able Archer 83 exercises, between both powers during the Cold War and in Cuba, where nuclear war was closest. In fact, only twice in history has a DEFCON 2 defense condition been reached in the United States.

The crisis covers the period between the discovery of the medium-range ballistic missile R-12 and R-14 of the Soviet Union (October 15, 1962) until the announcement of its dismantling and transfer back to the Soviet Union (October 28, 1962).

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