Which of the four major religions (Christianity, Islam, Hinduism and Buddhism) have killed fewest people?

Question:

Answer:

It's hard to say. Hindus have been killing people much longer then any of the other three that you listed followed by the Buddhist. Lately atheists, such as Stalin and Mao have been responsible for more deaths than any of the religions you listed.
Taking the period that all four religions have co existed, you have of course the crusades, where the numbers killed by each side was kind of a toss up. The mongols who were a mix of Buddhist, Muslim, Christian with a little Shamanism thrown in happily killed everybody. Of course you had the Chinese, Japanese and Korean Buddhist killing there own people and each other. Of course WWI was mostly Christians fighting except for the Turks, but then we have WWII, Korea Southeast Asia to balance that. So who knows.