"Why is Christianity so successful?", Well Because God Wants Us to be Successful,he wants to put us on display in front of the whole world and without him were nothing and the thing is with everything is that not everyone is saved from Jesus Christ and Its A Big Deal/Meaning of being a Christian God Gives us Grace sometimes but not all the time.
All these countries are part of the Commonwealth. The governments in each are all run on the same basis which is based on English system whereby the Prime Minister runs the affairs of the country instead of a President and with members of Parliament,