Samuel, you may want to take a look at 1st Kings 11:1-2
That is interesting, there Moabites are added to the list of Canaanite peoples. Which seems inconsistent.
However once again we can see that this was not a blanket rule, as Ruth was a moabitess and her marriage to Boaz is praised - because she chose to follow YHWH. And the issue with Solomon's marriages is once again that they would turn him away to other gods. So this does seem to reinforce that it is about religion rather than race.
ZecAustin said:
And what about the rules for marrying women captured in war?
I suppose it could be argued that this only applied to women from nations other than those on the mandatory "kill" list of Canaanites, but given that you only capture women when you're invading someone else's land, not defending your own, and their only invading wars were against Canaanites, these rules too only make sense if they apply to Canaanites. Which also reinforces that this must be about religion primarily.
This gets complex though because it is interrelated with other issues. Going further down the rabbit-hole...
The instruction to slaughter even Canaanite children is difficult to reconcile. However, we are told that in the time of Noah "there were giants on the earth in those days
and also later", when the fallen angels mated with human women. There were also giants in Canaan. It is possible that this was a re-emergence of the nephilim (fallen angel / human hybrids). If so, Canaan was infected with an evil bloodline. This bloodline could not be allowed to infect Israel because it could contaminate the bloodline of Messiah. The only way to eliminate it was to exterminate the Canaanites, hence the need to slaughter everyone.
But if marriage to Canaanites was permissible provided they converted, then that would suggest that there was not a Nephilim / fallen-angel-hybrid issue, and it was solely about religion. That makes marriages make more sense, but makes it harder to understand why they were instructed to kill even the babies, who couldn't lead anyone astray after false gods. An instruction to kill babies only makes sense in my mind if there was something intrinsically evil about those babies themselves.
Or possibly both issues existed, and YHWH knew in His wisdom that only those who were not infected with a Nephilim bloodline would convert to follow Him. In that case, Jericho was massacred to exterminate an evil bloodline, but not everyone in the city had that bloodline, Rahab did not, she converted and there was no problem bringing her into Israel...
My main point is that it gets complex when you try to reconcile everything.
And ultimately we can never understand everything perfectly - but it is good to try.