Chapter 19: Murders to be put to Death
Cities of refuge among the children of Israel are established in cases of accidental manslaughter, so that the one who committed the accident can flee that he might not be killed out of revenge. If the person is to be found guilty by two or three witnesses (verse 15), then they shall be put to death. Anyone who is a false witness shall be punished.
Out of the mouth of two or three witnesses, the word shall be established. This is one of the reasons that missionaries in the LDS church preach in pairs, and sometimes in trios.
Chapter 20: Laws of War
When the children of Israel are to go to battle, they are reminded to not be worried when the opposing army is bigger, because the Lord will stand by them. They are told to take care of unfinished business before they go to war, that they might be able to enjoy life in the case that they are killed in battle.
If the children of Israel or anyone goes to war upon a city that wants peace, and are genuine about this peace offering, you must respect it. However, if they want war, then they are commanded to smite all the males with their sword, and kill them in the city. Women, children and animals are to be spared and part of the spoils of war.
Israelites are commanded to “utterly destroy” the Hittites, Amorites, Canaanites, Perizzites, Hivites, and the Jebusites.