If - not a particularly likely scenario, but if - some kind of highly exclusive religion came about, it could have made the settlement of the New world much nastier. I mean, already you had the Western Empire and the Angles enslaving or warring against and wiping out some of the native peoples, plus the horrors that disease inflicted. But at the same time - with the Western Empire at least - other tribes were incorporated into the Empire, with many becoming citizens. Which the more open religious nature of the Empire allowed for. If the Empire followed some kind of exclusive monotheism...it'd have been much, much nastier.
I doubt the Dine would have become foederati, for example.
I doubt the Dine would have become foederati, for example.