Well, you have to ask yourself to what extent the geographical divisions are real, and to what extent they are within our imaginations, imposed by our thinking. As far as our modern conception of the east/west divide goes, I would point to the USSR and the Cold War as being the main reason most people think of there being a huge difference between east and west. There are of course other real differences. The split between the east/west Roman Empire, the corresponding split between Catholic/Orthodox Christianity, the fact that Eastern Europe is the limit of the Latin alphabet, the fact that some of the populations of Eastern Europe are descended from Central Asian peoples who migrated from the steppes.

Also, Europe is divided between North and South as well. Catholic/Protestant, Germanic/Latin, and so on.