Why was his decision to nationalize Iranian oil such a threat to global superpowers?
You have to go back to that time period in the early 1950’s. There had not been any leader of a poor country who had stood up to challenge the masters of the world in such a direct and important way. Mossadegh was essentially saying that the company [Anglo-Iranian Oil company now known as British Petroleum], that was richest, most lucrative property owned by Britain anywhere in the world, was actually not Britain’s property at all. He was saying that the oil under Iran’s soil belongs strictly to Iran. The British responded to this by complaining that Iranian oil was the private property of a British company and for Iran to nationalize it would essentially be theft of that private property. There has never been the leader of a country who decided to try to nationalize such an important resource in a way that so outraged not just Americans but even big countries around the world. What effect that had in Britain, of course, was obvious. Oil from Iran had been the basis for the standard of