Is it? Certainly the legal system of the western world is judeo-christian based but can you really say most of the western world is christian? Still? The religious right gets louder and louder (and more politically mobilised) but their per capita numbers are shrinking in most Anglo-Saxon societies. The most recent Australian census established that only around 50% believed in god and only a proportion of those are christian. I daresay it comes down to who you mix with, but I personally know hardly anyone who is (what I would call) a committed practising christian, and not many more who would call themselves believers in god, even a vague amorphous non-denominational god.
I guess this discussion ought to go on another thread but it's likely to be very contentious.
Well, something like 78% of Americans self-identify as Christian. If you head south to Mexico it is something like 98%. Much of central and South America is similar. Even a very secular place like Holland has numbers a bit above 50%. I think it is still safe to say that "most" of the Western world is Christian. North, Central and South America by themselves, population-wise, are going to really swing those numbers.