"Do not make a covenant with them or with their gods."
- Exodus 23:32
"It is not because of your righteousness or your integrity that you are going in to take possession of their land; but on account of the wickedness of these nations, the LORD your God will drive them out before you, to accomplish what he swore to your fathers, to Abraham, Isaac and Jacob."
- Deuteronomy 9:5
"Then they devoted all in the city to destruction, both men and women, young and old, oxen, sheep, and donkeys, with the edge of the sword."
- Joshua 6:21
During my edgy atheist phase I used to think that the Old Testament was repulsive and barbaric and that God was an evil brute for commanding genocide. Later I re-read the Bible and saw that the nations and populations the Israelites were exterminating engaged in things like human child blood sacrifices. Then I look to more recent human history, specifically the Spanish conquest of Aztecs–another people that preformed human blood sacrifices.
The Amerindians were blood-thirsty savages with unrivaled sadism. Instead of completely exterminating the Amerindians of Mesoamerica and repopulating their lands with people of their own race as the Israelites of the Old Testament would have done, the Spanish chose to miscegenate with the Amerindians. Look at the people this miscegenation produced! Go on some gore website and see the s— cartels in Mexico and Central America do! This is what people with Aztec genes do. They carve people's hearts out like in this video:
https://www.shockgore.com/watch/policeman-tortured-beheaded-and-his-son-flayed-alive_XEsowb4SaMPLKyb.html
If the Spanish had followed the war conventions of the Old Testament and completely replaced the Mesoamericans in the cultural and genetic sense, Latin America today would be like Spain the way the white communities of New England in the USA and Canada are like England. Low crime, wealthy, high IQ population and all the ways in which Spain is better than Latin America today. At worst it would be something like the wealthy parts of Argentina, Uruguay and Southern Brazil.
The moral of this story: Just because the information you need to be saved is in the New Testament, doesn't mean there isn't useful wisdom in the Old Testament that Christians can apply.