“They refuse to surrender and submit because it is their beliefs, their values, their faith, their traditions, their tribe, their God, their culture, their civilization, their honor that they believe they are fighting for in what is, after all, their land, not ours.”
Kill them all, then.
Only way to "win" is to go roman on them. Kill all the men and sell the women and children into slavery. Then salt the ground so nothing grows there again.
Otherwise, just accept that they are foreigners with foreign ideals. The Romans ended up doing that with the Germanic tribes.