The United Neptumousian Empire wrote:Constantinopolis wrote:Arch already answered this question very well, but I'd like to add to his answer. The big difference between Catholic and Orthodox numbers today is overwhelmingly due to Catholic expansion and missionary work in Latin America, Africa and Asia from the 16th century onward. Neither the spread of Islam in formerly-Orthodox lands in the Middle East, nor the rise of Protestantism in formerly-Catholic lands in Europe, made much of a difference by comparison.
Think of it this way: Even if the lands that Orthodox Christianity lost to Islam were still 100% Orthodox Christian today, their total population only amounts to 220 million people (Turkey + Syria + Lebanon + Israel/Palestine + Jordan + Egypt + Libya). That would only raise the Orthodox population to about 450 - 550 million overall. Still only about half of the current global Catholic population.
On the other hand, if the Catholic Church was still limited to western Europe and north-west Africa, then even if the Protestant Reformation never happened (and even if Islam never spread into formerly-Catholic north-west Africa), the total Catholic population today would only be... about 550 million. To be more exact, if you add together the Catholic and Protestant populations in Europe (i.e. assume the Reformation never happened), and then add to them the populations of Tunisia, Algeria, and Morocco (i.e. Islam never happened), then the number you get is precisely 545 million.
So, if you count the present-day populations of ancient Catholic lands and ancient Orthodox lands, they turn out to be about equal. It's what happened outside of Europe and the Middle East that ultimately made all the difference.
I'd failed to account for colonialism. Interesting, one can only wonder what things would be like if the Byzantine Empire had survived and began to colonize the Americas.
I'd find it really unlikely that the Byzantine Empire would colonize the Americas if they had survived. European colonialism arose from various different factors such the necessity of new trade routes, geographical proximity to Africa, and the development of capitalism; If the Byzantine Empire survived, than these factors would have changed drastically and they wouldn't have compelled the Byzantine Empire to do so. It was never a case of countries saying: "Hey, some free land. I'll take it!"