I've seen a couple AHs that have Cuba annexed into the United States. This raises an interesting question: could Castro have become the president in a timeline like this? Keep in mind that I know very little about his family history, when his family emigrated to Cuba, etc. Is this possible, or is it an ASB scenario?
Just a few points..
Assuming that during the American control/occupation from 1898 to 1901, the movement for independence is somehow derailed, and Theodore Roosevelt fully annexes Cuba in 1901 with the promise of quick admission as a state, and that he keeps his promise, and so Cuba becomes a state in 1908, together with Oklahoma, while Puerto Rico (after Cuba's precedent) becomes a state in 1912, together with New Mexico and Arizona, bringing the number up to 50 already before WW I.
According to Wikipedia, Castro's father came first to Cuba during his service in the Spanish Army - the returned to Spain after the war, but definitely tool up residence in Cuba in 1899. So this would be before the PoD.
If he has the same kids with the same wifes as IOTL, Fidel, born 1926, now in the State of Cuba, is a natural born citizen of the US. So there is no legal problem against it. How his life would go, and how permanent US control over Cuba would alter the wider history of the world, remains an entirely different question...
But, of course, AH purist's would argue that Fidel Castro would never have been born, or at least not as the same person, because with Cuba a state of the Union for more than 18 years, many details in the personal lives of his parents would be different, and therefore, the chances that they still have the exact same kids, is approaching zero... (This is called the
butterfly effect)