It is easy to understand why the Israelites wanted the Canaanites dead. Not from a biblical standpoint, of which I don’t have enough understanding to comment on. But from an economic and social standpoint. Assuming that the Israelites did indeed kill as many of the Canaanites as claimed.
At the time, the region was growing more crowded and competition for both land and resources was becoming more fierce. The Hebrews had two options, as far as I can tell:
- Travel (or remain) in Egypt and either be assimilated or become a separate underclass.
- Travel into Canaan and either be assimilated or take the land for themselves.
Assimilation is rarely desirable for such a large cultural group as the Hebrews would have been. If it would have been possible at all, seeing as how the Canaanites would likely have been hesitant to allow such a large influx of foreigners to dilute their population. So it was left that either the Canaanites or the Hebrews would keep the land.
The Hebrews did what anyone would have. It was a competition for resources and survival. It would be easy to pass a moral judgement on the fact, thousands of years afterwards, when I have never lived in a more savage world where I would face the threat, face to face, of the extinction of my tribe or my culture. But such a judgement would be pointless. And I am genuinely certain that we would react the same way that they did, if we lived in the same world that they faced.
As for how such things can be justified in a Catholic way, I don’t know. I do not know enough about the theological or scriptural understanding of the situation to comment on that. And seeing as how I avoid such moral judgements anyway, I am not the best person to ask.