What does Joshua 10:40 mean?

So Joshua took control of the whole southern region—the hills, the desert, the lowlands, and the mountain slopes. He didn’t leave anyone alive. He destroyed everything that breathed, just as God, Israel’s God, had commanded. Joshua 10:40 - Modern Text Bible

(This verse sums up the campaign: Joshua and Israel completely conquer the southern part of the land, following what they believed was God’s command to leave no survivors.)