One thing that really baffled me about Europe was just how much damn history there is. Like... Virginia, for as long as it's had political boundaries of the type I recognize/am required to study, has always been Virginia. West Virginia left, but for as long as it's been a state it's had kind of roughly continuous boundaries and such. That is so not the case in Europe. Any given spot was probably controlled by the Vikings and the Romans and the Normans and the Holy Roman Empire and god knows who else; one town could have been part of a dozen different political territories throughout it's history. I find this incredibly confusing.
So in light of this, I have no idea how this graph works, but I think it's kind of nifty all the same.