Final answer:
The event that led to the United States turning against Fidel Castro was the Cuban Revolution, which brought down the US-backed Batista government and led to Castro gaining power.
Step-by-step explanation:
The event that led to the United States turning against Fidel Castro was the Cuban Revolution, which brought down the US-backed Batista government and led to Castro gaining power. Initially, the US recognized Castro's revolutionary government in 1959, as he had spoken out against Communism. However, Castro's actions soon convinced Americans that his leadership was harmful to US business interests and that he was leading Cuba towards Communism.
Congress responded with sanctions, restricting travel to Cuba and banning the importation of Cuban products, which severely impacted the Cuban economy. Additionally, the failed Bay of Pigs invasion in 1961, authorized by the US to overthrow Castro, further strained relations between the United States and Cuba.
Overall, the Cuban Revolution and its aftermath led to the United States turning against Fidel Castro due to concerns about his leadership, Communist ideals, and the impact on US business interests.