And perspective plays a big part as well. WWII is now part of taught history, but I never viewed it as history because people I grew up with (my grandparents and their friends) experienced it first hand. Yet when our teacher read us a story about the racial segregation in the US after the war it felt more like history because I knew no-one who'd experienced it. Then when you look back at historical records a period of a hundred years seems so small you forget that people at the start of a century would likely never have even been met by those at the end.
When I first came to Australia I felt that it didn't have much in the way of historical buildings compared to the UK, but then even in the UK many buildings pale in comparison to the ages of things like the pyramids. We're unearthing more and more things from different cultures across the world as well, that we used to assume were primitive.
Yet it all still seems completely disconnected from our world today, despite the fact that everything has brought us to this point.