The Mosaic books of what Christians call the Old Testament contain many divine commands on war and descriptions of the Israelites following those commands on their way out of Egypt to the land of Canaan promised to them by God.  The theme of many of these passages is "cherem," utter destruction of a city and all living things in it.
 

7:1 When the Lord your God brings you to the land that you are going to occupy and forces out many nations before you-Hittites, Girgashites, Amorites, Canaanites, Perizzites, Hivites, and Jebusites, seven nations more numerous and powerful than you-

7:2 and he delivers them over to you and you attack them, you must utterly annihilate them. Make no covenant with them nor show them compassion!

. . .

7:16 You will overwhelm all the people whom the Lord your God is about to deliver over to you; you must not pity them nor worship their gods, for that will be a snare to you.

7:17 If you think, "These nations are more numerous than I-how can I dispossess them?,"

7:18 you must not fear them. You must carefully recall what the Lord your God did to Pharaoh and all Egypt,

7:19 the great afflictions you saw, the signs and wonders, the strong hand and extended arm by which he brought you out-thus the Lord your God will do to all the people you fear.

7:20 Furthermore, he will release the hornet among them until the very last ones who hide from you perish.

7:21 You must not tremble in their presence, for the Lord your God, who is present among you, is a great and awesome God.

7:22 He, the God who leads you, will expel the nations little by little. You must not overcome them all at once lest the wild animals overrun you.

7:23 The Lord your God will give them over to you; he will trouble them with great difficulty until they are destroyed.

7:24 He will hand over their kings to you and you will erase their very names from memory. Nobody will be able to stand before you until you annihilate them.

. . .

20:10 When you approach a city to wage war against it, offer it terms of peace.

20:11 If it accepts them and submits to you, all the people found in it will become compulsory servants to you.

20:12 But if they do not accept terms of peace but make war with you, then you are to lay siege against their city.

20:13 The Lord your God will deliver it over to you and you must kill every single male by the sword.

20:14 However, the women, little children, cattle, and anything else in the city-all its plunder-you may take as your booty. You may appropriate the spoils of your enemies that the Lord your God has given you.

20:15 This is how you are to deal with all those cities very distant from you, those that do not belong to nearby nations.

20:16 As for the cities of these peoples which the Lord your God is going to give you as an inheritance, you must not allow a single living thing to survive.

20:17 Instead you must put them under the divine curse-the Hittite, Amorite, Canaanite, Perizzite, Hivite, and Jebusite,-just as the Lord your God has commanded you,

20:18 so that they cannot teach you to do the detestable things they do to their gods and you thereby sin against the Lord your God.

. . .

21:10 When you engage your enemies in warfare and the Lord your God allows you to prevail and you take prisoners,

21:11 if you should see among them an attractive woman whom you wish to take as a wife,

21:12 you may bring her back to your house. She must shave her head, trim her nails,

21:13 discard the clothing she was wearing when captured, go to your house, and lament for her father and mother for a full month. After that you may have sexual relations with her and become her husband and she your wife.

21:14 If it should turn out that you are not pleased with her, then you must let her go where she pleases. You cannot in any case sell her; you must not take advantage of her, since you have already humiliated her.