Good question. The original proposition was in respect of a Muslim lying and why that may be justified as part of a moral code.

But who is out to kill whom?

Generally, little can be gained from war or destruction, so suggest fear between (religious) groups arises because of some critical need required for life is perceived to be under threat.

Once it starts others join because they see their society and/or way of life is under threat. Religion provides a code for living, a way of life, so is a binding social mechanism.

The original reasons for conflict may have been forgotten, but the mistrust between groups may linger.