The correct answer is C) the communist takeover in Cuba in 1959.
The event that represented a threat to U.S. national security interests during the 1950s was the communist takeover in Cuba in 1959.
The Soviet Union presence in Cuba, supporting the leadership of Cuban leader Fidel Castro, represented a threat to U.S. national security interests in the region. Cuba is so close to the Florida peninsula, and the presence of the Soviet Union on the island of Cuba worried the US government so much. This was one of the tensest moments between the United States and the Soviet Union during the Cold War years.