Matthew Poole and continuators on Deuteronomy 20:10

10 When thou comest nigh unto a city to fight against it, then proclaim peace unto it .

This seems to be understood not of the cities of the Canaanites, as is manifest from ver. 16, 17, 18. who were under an absolute sentence of utter destruction, Exod 23. 32, 33. Deut. 7. 1, 2. whence they are blamed that made any league or peace with them, Iudg. 2. 2. but of the cities either of other nations who injured or disturbed them, or commenced war against them, or aided their enemies, or oppressed their friends and allies; or of the Hebrews themselves, if they were guilty or abettors of Idolatry or Apostacy from God, or of sedition or rebellion against authority, or of giving protection and defence to capital offenders. See Gen. 14. Iudg. 20. 2 Sam. 20. &c.

Marginal references: 2 Sam. 20. 18.