5. The Cuban Exiles Theory
After the 1959 Cuban Revolution brought Fidel Castro to power, Cubans in their droves abandoned their country and immigrated to the USA. Many exiles had hoped to overthrow Castro and return to their homeland, something which may have come to fruition had it not been for President Kennedy's infamously-poor execution of the US-led Bay of Pigs Invasion in 1961, which backfired spectacularly. Many bitter Cubans blamed Kennedy for the failure to overthrow Castro, and some conspiracy theorists claim they were so enraged, they may have plotted to assassinate the President.