I don't want this to be mistaken for standing up for European colonialism, European colonialism is the greatest crime in world history, but the rationale wasn't as much "This land was ordained to us by God" (Well, it was a thing for Spanish and Portugese colonists) as it was "You aren't even real people and you can't own anything if you aren't a real person with a flag. Tallyho now be a dear and work to death for me"
Sure the church of England and the Catholic church spent centuries justifying genocide theologically, but it's not like secularism stooped the muurdering