C. F. Keil and Franz Delitzsch on 2 Samuel 2:27-28

2Sa 2:27-28

Joab replied, “If thou hadst not spoken (i.e., challenged to single combat, 2Sa 2:14),the people would have gone away in the morning, every one from his brother,” i.e., there would have been no such fratricidal conflict at all. The first כּי introduces the substance of the oath, as in 1Sa 25:34; the second gives greater force to it (vid., Ewald, §330, b.). Thus Joab threw all the blame of the fight upon Abner, because he had been the instigator of the single combat; and as that was not decisive, and was so bloody in its character, the two armies had felt obliged to fight it out. But he then commanded the trumpet to be blown for a halt, and the pursuit to be closed.