Another Medieval Monday, and something about national borders, since those seem to be quite relevant in Europe and the UK at the moment. The Middle Ages were the time when several of the nations that we know today coalesced in Europe. England came into being as a kingdom in 1055 (when they finally added York to the rest of it. The kingdom of Northumbria, meaning everything north of the Humber in the east, was one of the last bits to be added), even if it and Wales had already been under Roman occupation. France became something approaching a coherent state under Philip Augustus in the 13th/14th centuries. Germany and Italy...
That's where this breaks down a bit. Germany was still playing at being the Holy Roman Empire (although Charlemagne's legacy had at least as much to do with France). Italy was a series of city states, nominally within the HRE, but really not unless people like Frederick Barbarossa nipped down with an army to tell them that they were. Most of the countries in the East of Europe had to put up with the Golden Horde Mongols putting any ambitions they had for statehood on hold.
Even for places that sort of were in existence, their borders weren't what we're used to. England and Wales only came together in the late 13th century, and wouldn't be joined to Scotland for another four hundred years. Scandinavia seems to have been somewhat closer to its future boundaries, but places like Spain were still a mess of separate kingdoms with their own languages. They weren't the modern nation states, because the idea was only just starting to come together. At the start of the period, there were kings "of the Franks" rather than "of France", because the idea of the place didn't exist. Borders could shift as lords gave their allegiances to different people, but also as their power shifted. In France again, Normandy was all but a separate country, with stronger connections to England's rulers thanks to William I, until Philip Augustus stole it while King Richard was out on crusade. Aquitaine could easily have been a part of that larger Angevin Empire had Eleanor of there not divorced the English king only to end up marrying the French one.
I suppose this is a message to two lots of people. The first is to any politician who tries to lean on history for the "natural" shape or size of a country. They've been practically every shape and size you can imagine through history, I can promise you. The second is to writers who make up countries (fantasy writers like me do this a lot). There's a tendency in novels to see those as essentially static, or just to reference some kind of great empire in the past that ruled everything, and since then, it's broken up into... well, modern nation states in all but name. In fact, the picture was probably far more complex, and always shifting.