I'd say, within all history, granted I have not read on ALL wars, but many that most people do not read about, I'd say about 5%. Much of those were fought between the Roman Catholics and Protestants, the French Huguenots and Crusades, the Ottoman Empire, the rise of Islam was bloody. The 30 Years war in the 17th century cannot be understood properly if one attempts to make a religious war only stance (I wont get into why). The wars that took place in latest era are not religious wars at all, thought there are strong ties to it, it still cannot be understood as being a religious war. When greed is accounted for, I think it takes the largest part of the reason for war. Perceived retribution another part, and religious reasons last I would say.