I was teaching my 11-year-old daughter about the 8th century in Church history yesterday, and I was explaining the expansion of Islam in the East. I went on to talk about the fear in Europe that Islam would overwhelm the West like it did the East. This fear was present for almost 800 years (and is a major, yet under-appreciated, factor in the calling of the Crusades). This map does a great job of showing the spread of the major religions around the world – see how quickly Islam grew:

In my class with my daughter, I ended up going on a tangent about the fact that Islam might be able to succeed today through demographics where they failed by force during the middle ages. It should be common sense (but unfortunately isn’t) that those cultures which have a lot of kids will eventually overtake those who do not. Europe, are you listening?