Overall, the lessons of history teach that geographically large, wealthy, socially advanced empires don't actually survive all that long on average. They are complex systems with lots of moving parts, and various unexpected stressors can break essential components in unexpected ways. Major changes to the labor force, migration and productivity are very frequently the type of stressor that breaks empire systems.
The EU is a form of empire, that had many flaws from it's inception. The British Empire we believed had already fallen and was on the mend after WWII, had maybe found it's place in the EU, but the reality is looking like it still had further left to go to hit rock bottom. (If we look at the map of the vote it resembles Britain circa 1700, before the rise of British colonialism.)
Likewise, in the USA the American empire has hit the peak of it's capacity for expansion and economic dominance and is starting to get a taste of what the cracks in empire look like. This truly massive scale democratic republic is a real achievement but it's unclear what happens in a system like this at this scale. We may have simply exhausted the limits of a republic to project power, expand wealth and still maintain political harmony at home. The population's awakening to these changes, coupled with feeling the stress of labor shifts, is manifesting in political upheaval.
Anyhow I'm no expert in history or government but I don't believe it's out of the question to assume this is what it feels like to be embarking into the darker bits of history. Personally, I'm accepting that Asia will become the dominant economic driver for the remainder of my life and plan on embracing that from here out