They came from a Christian culture, and when they arrived in a new place, they noticed that some people didn't have Christianity, and so they asked themselves the following question: what have they got instead of Christianity?
Now there's a difficulty with proceeding in that way, which is that Christianity is extremely, even on that list, it's an extremely specific tradition.
Now that's a very specific and particular history that Christianity has, and not everywhere is everything that has ever been put on this sort of list like it.
And while I found I knew nothing about these faiths at all -- despite my own intensely religious background, I'd seen Judaism only as a kind of prelude to Christianity, and I knew nothing about Islam at all.
しかし この地図では キリスト教 イスラム教 仏教が ー さらに細分されています これでは細かすぎます 