God is a man of war.
The Lord is a man of war. Exodus 15:3
He teaches us how to fight wars.
He teacheth my hands to war. Psalm 18:34
Blessed be the LORD my strength which teacheth my hands to war, and my fingers to fight. Psalm 144:1
Sometimes he commands us to commit complete genocide on our enemies.
And the LORD said unto Moses, Fear him not: for I have delivered him into thy hand, and all his people ... So they smote him, and his sons, and all his people, until there was none left him alive: and they possessed his land. Numbers 21:34-35
And Moses was wroth with the officers ... And Moses said unto them, Have ye saved all the women alive? ... Now therefore kill every male among the little ones, and kill every woman that hath known man by lying with him. But all the women children, that have not known a man by lying with him, keep alive for yourselves. Numbers 31:1-18
And the LORD our God delivered him before us; and we smote him, and his sons, and all his people. And we took all his cities at that time, and utterly destroyed the men, and the women, and the little ones, of every city, we left none to remain: Deuteronomy 2:33-34
If thou shalt hear say ... Certain men ... saying, Let us go and serve other gods, which ye have not known ... Thou shalt surely smite the inhabitants of that city with the edge of the sword, destroying it utterly, and all that is therein, and the cattle thereof, with the edge of the sword. Deuteronomy 13:12-15 But of the cities of these people, which the LORD thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth: But thou shalt utterly destroy them ... as the LORD thy God hath commanded thee. Deuteronomy 20:10-17
And they utterly destroyed all that was in the city, both man and woman, young and old, and ox, and sheep, and ass, with the edge of the sword. Joshua 6:21
So Joshua smote all the country of the hills, and of the south, and of the vale, and of the springs, and all their kings: he left none remaining, but utterly destroyed all that breathed, as the LORD God of Israel commanded. Joshua 10:40
For it was of the LORD to harden their hearts, that they should come against Israel in battle, that he might destroy them utterly, and that they might have no favour, but that he might destroy them, as the LORD commanded Moses. Joshua 11:20
Thus saith the LORD of hosts, I remember that which Amalek did to Israel, how he laid wait for him in the way, when he came up from Egypt. Now go and smite Amalek, and utterly destroy all that they have, and spare them not; but slay both man and woman, infant and suckling, ox and sheep, camel and ass. 1 Samuel 15:2-3
But sometimes he commands us to kill all the males and non-virgin females -- and enslave the rest.
And the LORD spake unto Moses, saying, Avenge the children of Israel of the Midianites ... And they warred against the Midianites, as the LORD commanded Moses; and they slew all the males. And the children of Israel took all the women of Midian captives, and their little ones ... And they burnt all their cities.
When thou comest nigh unto a city to fight against it ... And when the LORD thy God hath delivered it into thine hands, thou shalt smite every male thereof with the edge of the sword: But the women ... shalt thou take unto thyself; and thou shalt eat the spoil of thine enemies, which the LORD thy God hath given thee. Deuteronomy 20:10-17
God swears that he'll be in a war with Amalek forever.
The LORD hath sworn that the LORD will have war with Amalek from generation to generation. Exodus 17:16, Deuteronomy 25:19
And although Jesus was inconsistent on the topic, he sometimes agreed with his dad on war.
Think not that I am come to send peace on earth: I came not to send peace, but a sword. Matthew 10:34
He that hath no sword, let him sell his garment, and buy one. Luke 22:36