Since I started watching this show I've been fascinated by the Gems, however the Earth looking the way it does would have changed more than just human history, it would have changed the ecology of the Earth as a whole and the fact that it took place within history as in human writing was well on its way 5000 plus years ago. The show seems to down play it, but A LOT would have changed!
Steven lives in the Americas (this concept shouldn't even exist as I feel the landmasses would have way different names) and the place he resides in seems to be govern by the U.S. government, the only other country that I know exist in this continuum so far is Canada; by the way how many states form the United Sates in the SU universe anyways? I couldn't even begin to guess what states exist when Pennsylvania is called Keystone (way less cooler name), NYC somehow is also Las Vegas-esque and is called "Empire City", apparently Kansas is Hollywood-like. I doubt we could ever recognize nearly all of Earth's/humans’ political, ecological and environmental landscape. Asia now has a gulf where Siberia would be, something very similar to Hudson Bay in N. America only way bigger, so I can only guess what people and other animals in the Siberian Bay could live like. The horn of S. America (or whatever is called as I don't know if it has one) is mostly in the middle of what would be the southern Atlantic, Africa and Europe are tiny and Australia is what I would describe an archipelago; did Europeans colonized some of the world? Is the Sahara a thing in northern Africa? Also not to mention that all these geological changes happen relatively recent, I mean we are messing with our planet now and is causing a lot of trouble (not just climate change) what could possibly be the consequences of the Gem’s terraforming? All this at a simple glance, how about anyone else?
All those Gem corruptions should have harmed us way more as no matter what the Crystal Gems couldn't possibly be able to help all of humanity for the last 5000 years! What about all the Gem tech?! I mean we have a hard time accepting humans build the pyramids (irrelevant of locations) as some really think we had extraterrestrial help with those. Man, there is just no end to how different that world would be compared to ours.