18. Cuba
As I said before, it's no secret that Jack Kennedy was no friend to Fidel Castro; in fact, it's arguably during the Kennedy Administration when tensions with Cuba reached a boiling point with the infamous Bay of Pigs Invasion and the subsequent Cuban Missile Crisis. So naturally, when Kennedy took a barrage of bullets in 1963, the timing was questionable. Interestingly enough, Oswald was arrested shortly before the assassination for passing out pro-Castro literature in the streets of New Orleans and sought refuge in Mexico City's Cuban embassy shortly afterwards, and allegedly announced his dastardly intentions for the embassy to hear. There are varying forms of this particular conspiracy theory. There are those who believe that Oswald acted alone but in the interest of Cuba, those who believe that Castro had tacitly allowed Oswald to assassinate Kennedy (meaning he knew of the attempt and did nothing to stop it), and of course those who believe that Cuba had directly ordered Oswald to assassinate Kennedy in order to prove his loyalty to the Castro regime during his Mexico City visit.