First- I think organized religion is the cause of conflicts between peoples, not belief in God...Allah and God are the same- Mohammed and Jesus Christ are not
This is a really good point.
That said, I think I should clarify something. Religion itself doesn't lead to people killing other people. Religion just acts as a convenient in-group/out-group indicator in pre-existing sectarian conflict. If you're a Shia militant in Iraq, you're not killing Sunnis to avenge the Prophet's grandson Hussein's death at the treacherous hands of Yazid, you're trying to maximize the Shia share of the goods in post-conflict Iraq and trying to minimize and steal Sunni influence. You see a guy named Omar, you know there are basically no Shia Muslims named Omar, you kill Omar and take his stuff.
Similar dynamic in Northern Ireland. People don't kill each other over the literalism of transubstantiation. They use it as a convenient marker for who's on which side.