The history of the world would be different, to be sure. That’s fine with me. I don’t know what the end result would have been. You take westward expansion as a given—you are a believer in “manifest destiny” I take it. I am not. I can see other outcomes. Maybe there would have been other confederacies. So what? Maybe we wouldn’t have been involved in Europe’s wars. So what? The US civil war wouldn’t have happened at all. No Hawaii or Alaska? So what? No superpower? So what?
The standard of living in the world today and certainly in the US would be lower. WWII, for all the death and destruction it brought, also ushered in a long bought of peace and forced structure and civility among many nations.
You and I may or may not exist today and this continent may have been conquered by tyrannical Superpowers. Check the rise and fall of the Roman Empire. Once the feeding and conquering of nations and people proves successful for the wealth and sustainability of a Dictatorship, it needs to continue to feed.
I say it is a huge deal and the world, including America, would not be as great of a place. Call me patriotic, but I enjoy with confidence our status as the greatest nation on earth, even with our current and past flaws.