To understand Brexit one must understand Edward I and his progeny. Frankly, they started this process off. We Americans have little understanding of history; ours is but some two hundred and forty years. Edward I brutally attacked and hacked his way through Scotland, Wales and Ireland while having occupation rights on most of what we now know as France. His son, Edward II, was most likely the worst King ever, and that include John I and Richard III. His bumbling started the Hundred Years War, yes folks, it was a hundred plus years. Then Edward III managed to intensify this war, and despite the small period with Henry V, the English hacked and slaughtered their way through the Fourteenth and Fifteenth centuries.
So perhaps the roster, well you get the point. Also for almost all Americans who have never lived in Europe, that includes any diplomat or corporate type since they are just ex-Pats, they have no idea how a few thousand years of history still has a day by day impact. I recall the terror in my Czech partners in visiting the Austrians, and the Austrians dislike of the Italians and the French dislike of everyone, and the fact that everyone dislike Germans. Welcome to Europe.
The final issue is that Democracy has a strange effect. People vote and unless you are listening to the people you can get surprised. Will the French be next?
Then there is Russia. Having spent time there and looking at Russian from a non-Kennan like perspective, namely looking at Russia in a long term historical context, one sees the Russians having a point. Between Napoleon and Hitler they have a concern as to threats on their borders. I also believe that includes China and frankly should include North Korea. Eastern Russia, Vladivostok and environs has at its borders an unstable nuclear enabled state. That may be a balance for China but it is an unstabilizing factor for Russia.
The challenge for the next US President will be to understand these complexities. All the way back to Edward I and even before! One should remember why the Metropolitan of Moscow will not convene with the Bishop of Rome. Think about it.