This world spins in revolutions, baby, spirals and turns, and it's this constant motion that produces patterns that can be seen in humanity, or civilization if you rather. Arguably civilization or advancing society can be traced, moving with time from east to west.
Lets start with the ancient Chinese culture.
Mongols, Vandals and Huns surge to the west find a space to live and on their way stop and loot everything that's in their way. They are ticked, they are forced out of their homeland and made to seek out new natural resources or take it from other people. Meanwhile in the west. Founded not in Rome, but in Germany, not by religious zealots but by pagans that at first resented and outlawed Christianity, and were hardly the 'Empire' of their namesake because of in-house fighting, jealousy and sibling rivalry. During this time we have a huge addition and mixing of the gene pool.