There are more Roman Catholic Christians alive today than there have ever been non-Catholic Christians - alive or dead - in all of history.
Catholicism.
Christianity - and the particular denomination is Catholicism
Catholicism
... Catholicism is a religion itself. The only Catholic religion is Catholicism.
south America
Catholicism is probably way up there.
Catholicism
Catholicism and Orthodox Christianity
Protestantism and Catholicism are both equally the most popular. In southern Europe, Catholicism tends to be more dominant, while in the north, Protestantism is.
Christianity, mainly catholicism
Catholicism became the official state religion of France in 496 AD when Clovis I, the king of France at that time, changed religions from paganism to Catholicism.
Roman Catholicism, it might still be the most popular.. :)