The Torah tells us (Deuteronomy 7:22) we could not kill the through-and-through wicked Seven Nations of Canaan quickly because G^d only will deliver them piecemeal. Then it says something amazing. The slow pace is because a fast removal of all of them would make that wild animals would take over the created vacuum before we could settle the Land ourselves.
In other words: You’d think this is unfortunate, but it’s really for the best.
G^d didn’t need to tell us. He could have demanded trust in Him. But He explains why this is the best possible scenario. G^d doesn’t demand from just everyone blind trust.
In fact, it says (Deuteronomy 7:17) that when you’d worry about a stronger enemy, don’t be scared. Just remember what G^d did to Pharaoh and all the Egyptians. It could have said: Don’t consider the strength of the enemy. But it says: If you are among those scared, I’ll reassure you out.
Similarly, G^d says to those worrying about what we’d eat the Sabbatical Year, I’ll give you a threefold harvest (Leviticus 25:20). He doesn’t say: Just trust in Me. He spells out guarantees to those who worry. (Those who don’t worry don’t have three times as much to carry home, store, and kook. For them, food will have thrice the normal nutritional power.)
Introduction: The Torah is not a history book. Events it describes could have happened precisely or not exactly as told. What is certain is that the lessons contained are perfect, eternal, and to be taken to heart.
So, these genocides may never have happened and are neither recommended. Rather, for the Jewish ear, it means: Don’t be too naive.
Jews are mostly nice naive people who dislike murder and violence and assume that everyone is as benevolent as us. We had to be, to be able to show the world what G^d expects of humans. Perhaps, therefore, we are told to have no mercy on the most wicked. Niceness will not always cut it, and projecting our peaceful mindset onto others could be dangerous.
(Alternatively, one rabbi suggests, we have the worst character of all and need the Torah to make humans out of us. It’s always nice to stay humble. We do see Jews who threw off the yoke of Heaven behave worse than terrible Atheists. But that might not reveal our initial wickedness. Rather, it could show that a vacuum in holiness is quickly filled up with evil.)
This idea of going slow to prevent wild animals from taking over might also have a less literal meaning, I’d suggest. Maybe this also comes to tell us not to be too forceful, or the opposition will be fierce, like wild animals.
Just similar to the idea of the Rabbis (on Deuteronomy 20:19) that we should allow citizens of beleaguered cities to flee. So that they will not fight to the death no matter what and to save as many lives as possible.
It could even mean we’ll meet our enemies slowly so that they can learn to be our friends. To give up being our wild, vicious haters.
I’m not saying that’s how we should always act. First of all, let’s not be naive. But we might keep in mind that potential friends could be among the most wicked. Don’t sweat making new friends in strange places.