Let's be specific. Since the context of this question as it relates to our original conversation indicates you mean Christianity when you say “religion” and the Bible when you say “a book,” I can say without hesitation that the only people murdered because of the Bible, are Christians who were murdered because they were Christians. And the actual number is probably more like billions, not millions, of Christians murdered for their faith since the birth of Christianity. In fact, Christians are the most persecuted religious group in the world. Hundreds of thousands of Christians are being denied the most basic of human rights, they are tortured, beaten, imprisoned and even killed each year simply because they are Christians and will not renounce their faith.
When it comes to those who have been killed “over a book” as you say, I can honestly respond that Christianity has not murdered a single individual because of the Bible. Again, this is not to say that murders have not been committed in God's name by people who claim to be Christians, but according to God's Word (1 John), they were not true Christians, but “pseudo-Christians,” those who claim to be Christians, but aren't. They will do the right things and say the right things up to a point, but then their true nature comes through. To blame Christianity for the actions of pseudo-Christians, is the same as blaming all of Law Enforcement for criminal acts committed by phony cops.