I was having a discussion on another forum, and this question came up. When you look at major religions today, it seems incredible that 1500 years ago, it was reportedly possible for St Patrick to convert Ireland from their traditional beliefs to Christianity. How did he do it? Christian missionaries have had similar successes with, say New Guineans in more recent times, reportedly telling them to burn their "pagan artifacts" and being obeyed. The Christianization of Iceland seems even more bizarre, seeing as it was done largely democratically, and with the decision that the country should become Christian being made by a Pagan priest called Þorgeirr Ljósvetningagoði. My best guess was that most societies that switch religions are converted by a combination of awe at the missionaries' technology/fine clothes/weapons, and that many of the old religions had never previously had to compete with other religions by means of theological debate, at which missionaries were well practised. It may also help if the society has had a recent spate of severe hardships. Can anyone provide a better, or at least better researched, answer?