Bible
Why did God order people to be killed in the Old Testament?
Some Old Testament passages describe God commanding Israel to destroy entire cities during the conquest of Canaan. Read plainly, that's difficult to sit with. Pretending otherwise wouldn't be honest.
Christian scholars read these texts differently. Some see them as a specific, unrepeated act of judgment on societies the text describes as deeply corrupt—not a general model for warfare. Others point to something else: ancient war accounts routinely used exaggerated "total destruction" language for battles that clearly weren't total. The same "destroyed" peoples show up again later in the same books. That suggests the wording is closer to ancient battle rhetoric than a literal head-count.
Neither view fully removes the difficulty. Most Christians who take this seriously don't claim a fully comfortable answer. It's more honest to say that plainly than to pretend the tension is resolved.
Bible quotations in these answers are generally taken from the Christian Standard Bible®, Copyright © 2017 by Holman Bible Publishers. Used by permission. Christian Standard Bible® and CSB® are federally registered trademarks of Holman Bible Publishers. Some biblical wording may be paraphrased or follow other translations.