Christianity's contribution to western civilization?

[Mental flatliner]

First of all, I'm pretty sure that there are only 2.1 billion Christians, roughly 1 billion Muslims, and fewer than 0.1 billion Jews. That brings you up to 3.2 billion out of about 7.1 billion people in total. Not quite 56%, I'm afraid. Islam spread its message mostly by conquering everyone and forcing them to convert. Christians did a bit of that too, but not nearly as much. There wouldn't be nearly as many Muslims if they weren't so violent.

The first rule in any academic pursuit is to have the best sources.
Mine is the CIA World Factbook, sponsored by an organization with offices in almost every nation on earth and billions in resources (and nearly devoid of information bias).

According to them, these are the numbers:

Christian 33.39% (of which Roman Catholic 16.85%, Protestant 6.15%, Orthodox 3.96%, Anglican 1.26%),
Muslim 22.74%,
Hindu 13.8%,
Buddhist 6.77%,
Sikh 0.35%,
Jewish 0.22%,
Baha'i 0.11%,
other religions 10.95%,
non-religious 9.66%,
atheists 2.01%

My calculator says 56.35%.

As for your premise that Islam is spread by murder, you've suffered a logic fail. Dead converts aren't counted in the above percentages. The worst you can say is that Islam is therefore spread by breeding (the take land, kill the inhabitants and then start breeding), but they are evangelical in nature as well, and this did come from Christian influence of Mohammed.

(As a rule, I never allow the atrocities committed by a few thousand to speak for over a billion. That would be prejudicial, now, wouldn't it? You have yet to explain how Islam spreads in free non-Muslim countries.)

[Andrew]

I don't mean that no one converts to Islam except on pain of death. I'm just saying that if the Ottoman Turks, et al. hadn't tried to conquer the whole of Europe and hadn't converted people on pain of death in many places, there wouldn't be as many Muslims today. Forced conversions were not the case everywhere, and not all conversions were forced. Those practices gave them a huge boost of numbers though.

[Mental flatliner]

I don't mean that no one converts to Islam except on pain of death. I'm just saying that if the Ottoman Turks, et al. hadn't tried to conquer the whole of Europe and hadn't converted people on pain of death in many places, there wouldn't be as many Muslims today. Forced conversions were not the case everywhere, and not all conversions were forced. Those practices gave them a huge boost of numbers though.

Conversion by force is never the rule; it's actually not really even possible.

That's why Russia is more than 80% Christian (because Russians were forced into atheism for 3 generations and the moment Glasnost began, suddenly 80% of the people started celebrating Easter).