When Castro came to power in the mid 1950s the US was initially glad  
to be rid of the corrupt Batista regime. But the revolution was quickly 
followed by reprisals, imprisonments and deaths by firing squad. Then 
Castro's communist leanings became apparent as he started nationalizing 
private industry. Relations rapidly soured. When he allowed the Russians
 to secretly put missiles in Cuba, the crisis came to a head. The 
Soviets relented and an unsteady peace has been in force since. The US 
didn't help much with the ill-advised Bay of Pigs invasion.