"Cameron encouraged us to expect that brexit would start world war three, are you saying he promised another war?"
While for sure the Remain campaign made a few howlers, this isn't really one of them. Cameron merely suggested that there would be an increased risk of destabilisation in Europe if we left the EU, and subsequently it broke up. This neither promises, nor gives reason to expect, World War III, and it was a massive misrepresentation of what he was saying. It's not clear that the risk is quantifiable anyway, let alone the change to it, but there was never a threat of WWIII.