"You're really going to argue that 2,000+ years of fighting in one area was surassed by WWI alone?"
Yes, because they weren't fighting for 2,000 years (there were several extended periods of relative calm, for example the Ottoman and Byzantine periods) and because the populations involved were generally small.
"Over the Holy Land. That's ONE of the many, many, MANY conflicts over the region in its history."
The Crusades were not one war. They were a series of wars spanning several centuries. And I don't know where these numbers come from. 3 million is absurd. Medieval sources tend to exaggerate sizes of armies. The armies the combatants carrying arms were never more than 35,000 in any singular one. In the first crusade the crusaders had 30,000 infantry and 4,500 cavalry. And furthermore, the Crusades were not all about the Holy Land. The 4th crusade involved Constantinople, and the 5th Crusade involved Egypt.
Let's assume based on available estimates that each side fielded around 35,000 men, which seems to be about average. Let's assume a very high casualty rate -50%. Over 9 wars that still wouldn't even touch 400,000 dead, let alone 3 million.