Final answer:
Fidel Castro took power in Cuba in 1959 and his immediate actions such as nationalization of American-owned businesses and establishing ties with the Soviet Union upset relations between Cuba and the United States.
Step-by-step explanation:
Fidel Castro took power in Cuba on January 1, 1959 after overthrowing the regime of President Fulgencio Batista. Soon after taking power, Castro implemented a series of actions that upset relations between Cuba and the United States. These actions included the nationalization of American-owned businesses and properties in Cuba, agrarian reform that seized land belonging to American companies, and establishing diplomatic ties with the Soviet Union, which was seen as a threat by the United States during the Cold War.
Learn more about Cuba-United States relations