This verse seems to leave no room for mercy. Was there ever an opportunity for peace?
The laws of war in Deuteronomy show a stark contrast between cities outside and inside the promised land. For distant cities, Israel was to offer terms of peace first. If accepted, they would live and be tributaries. However, for the Canaanite cities, the command was different. As Poole notes, this severe action was a 'just punishment of their obstinate refusal of peace offered.' God's judgment was severe because these nations had long rejected His grace and continued in sin. Yet, even within this harsh command, there's a framework: an offer of peace preceded the conquest, and specific distinctions were made (women and children were spared in most cases, as Calvin points out).