Jamieson, Fausset and Brown on 2 Samuel 20:18-20

18-20. They were wont to speak in old time--The translation of the Margin gives a better meaning, which is to this effect: When the people saw thee lay siege to Abel, they said, Surely he will ask if we will have peace, for the law (De 20:10) prescribes that he should offer peace to strangers, much more then to Israelitish cities; and if he do this, we shall soon bring things to an amicable agreement, for we are a peaceable people. The answer of Joab brings out the character of that ruthless veteran as a patriot at heart, who, on securing the author of this insurrection, was ready to put a stop to further bloodshed and release the peaceable inhabitants from all molestation.

2Sa 20:23-26. David's Great Officers.