Why is the United States so concerned about Cuba and communism taking hold in this country?

Answer: They are afraid of a middle crisis!

Explanation:

It shows that one disagreement can lead to assassination attempts, resulting in nuclear showdowns. Not only did the leaders of both countries disagree with each other, but Cuba was communist while the US was capitalist. Cuba scares the United States because of the threat of communism, as proven by the alliance with the Soviet Union - who the US already disagreed with, and also the Cuban Missile Crisis. That incident has left the US wary of what Cuba may do in the future and, although they seem to be patching up their relationship, no one knows what will happen between them in the future.