Christianity is an incredibly influential world religion today and throughout history. While most people in the the first world see Christians as somewhat annoying charity workers who preach a little too much, that view is not how it has been throughout history.
In general, killing Christians was practically the national sport of many nations during history. This was often due to the practice of non-violence or other controversial tenants of their belief. It is a wonder that the group is still alive.
My question is, how would you get a majority Christian world? What would it be like?
The way I would kick-start Christianities growth would be to delay or prevent the fall of the Roman Empire. Christianity was starting to get real popular before the Empire fell.
I believe the world would probably be more peaceful, due to the belief of "love your neighbor". But, even religion can't stop human nature.