No combustion engine. We still have the internet (though it took longer to propagate), so we can still communicate with people on the other side of the world, but to actually meet any of them would take many weeks or even months of travel. Other countries (outside of our immediate neighbours) still seem like exotic, mysterious places, with customs and cultures far removed from our own.

I don't know if it would work like that, but that's as far as I've gotten in five minutes of thought...