So often is this sentiment heard in the best sellers from Richard Dawkins to Sam Harris that it has almost become a proverb. It is said so often that people believe it without question.
But, in fact, religion does not cause war. If you are an atheist, I ask for your intellectual honesty in evaluating this question. You have every right to believe what you will, but we should all be honest and not sling mud where it is not warranted. Laying war at the feet of religion is just not honest, warranted, fair or accurate.
War is people (usually men) fighting, usually for a bit of territory or desired resource. One party wants something another party has. The leader of the first party will use whatever he can to galvanize his entire party, usually connecting to any group identity he can think of, which includes but is not limited to ideology, nationality, ethnicity, class and yes, religion.
War is two groups (of any definition, but of which the group designation is incidental) fighting over something one has and the other wants. Blaming only religion is as incorrect as blaming only ethnic groups, ideologues, persons identifying with a certain country or class struggle.
The two most destructive wars in history, World Wars I and II both had nothing to do with religion. WWI was the unfortunate culmination of dangerous levels of Nationalism. In WWII Hitler used nationality and ethnicity to galvanize his group to take what he wanted that others had: the whole of Europe. The millions who died under Communism were under a specifically atheistic ideology that explicitly proscribed religion and decried it as a delusion.
All wars in American history from the Revolutionary War, the Civil War, the Mexican War, the Spanish-American War, and the World Wars all had absolutely nothing at all to do with religion.
Ah, but the major one cited by atheists is the Crusades. Once again though, one group (this time, yes the Christians) galvanized...