JFK was assassinated because he was going to shut down the war in Vietnam - a war that brought the ruling powers $500 billion in armaments sales
Kennedy’s National Security Action Memorandum #263, October 11, 1963: ordered 1,000 men home from Vietnam by the end of 1963 and all U.S. personnel out of Vietnam by the end of 1965.
Noam Chomsky, in his book, Rethinking Camelot: JFK, the Vietnam War, and US Political Culture, argues that Kennedy was not planning to withdraw from Vietnam.
However, on December 23, 1997 it was announced that 800 pages of Joint Chiefs of Staff records had been made public the day before by the government's Assassination Records Review Board. Those declassified government documents show that weeks before his assassination John F. Kennedy told his military leaders to draw up contingency plans for a U.S. withdrawal from Vietnam, following the 1964 presidential election.