1 Samuel 27:9

9. David smote the land What was the occasion or reason of this terrible slaughter we are not informed, but probably roving bands from these tribes had made incursions into the land adjoining Ziklag. Compare 1 Chronicles 12:21. The question of Achish, in 1 Samuel 27:10, seems to imply that David was wont to make such predatory excursions; and some have sought to justify him in this slaughter on the ground that these nations were under the curse of God, and the Israelites were divinely authorized to exterminate them. But this was no sufficient warrant for David, while a fugitive from his native land, and without special instruction from God, to undertake the work on his own responsibility. If any apology is to be offered, it is the supposition that these tribes were disturbing the country by their lawless raids for plunder.