You may recall that the Israelites killed everything that lived in the city of Jericho and another town and now I find there are two other savage incidents, this time in the Book of Samuel:
1 Samuel 15:13-18 (New International Version)
13 When Samuel reached him, Saul said, "The LORD bless you! I have carried out the LORD's instructions." 14 But Samuel said, "What then is this bleating of sheep in my ears? What is this lowing of cattle that I hear?" 15 Saul answered, "The soldiers brought them from the Amalekites; they spared the best of the sheep and cattle to sacrifice to the LORD your God, but we totally destroyed the rest." 16 "Stop!" Samuel said to Saul. "Let me tell you what the LORD said to me last night." "Tell me," Saul replied. 17 Samuel said, "Although you were once small in your own eyes, did you not become the head of the tribes of Israel? The LORD anointed you king over Israel. 18 And he sent you on a mission, saying, 'Go and completely destroy those wicked people, the Amalekites; make war on them until you have wiped them out.'
1 Samuel 22:11-19 (New International Version)
11 Then the king sent for the priest Ahimelech son of Ahitub and his father's whole family, who were the priests at Nob, and they all came to the king. 12 Saul said, "Listen now, son of Ahitub." "Yes, my lord," he answered. 13 Saul said to him, "Why have you conspired against me, you and the son of Jesse, giving him bread and a sword and inquiring of God for him, so that he has rebelled against me and lies in wait for me, as he does today?" 14 Ahimelech answered the king, "Who of all your servants is as loyal as David, the king's son-in-law, captain of your bodyguard and highly respected in your household? 15 Was that day the first time I inquired of God for him? Of course not! Let not the king accuse your servant or any of his father's family, for your servant knows nothing at all about this whole affair." 16 But the king said, "You will surely die, Ahimelech, you and your father's whole family." 17 Then the king ordered the guards at his side: "Turn and kill the priests of the LORD, because they too have sided with David. They knew he was fleeing, yet they did not tell me." But the king's officials were not willing to raise a hand to strike the priests of the LORD. 18 The king then ordered Doeg, "You turn and strike down the priests." So Doeg the Edomite turned and struck them down. That day he killed eighty-five men who wore the linen ephod. 19 He also put to the sword Nob, the town of the priests, with its men and women, its children and infants, and its cattle, donkeys and sheep.