Offhand I can think of at least four. I would suggest these as options to consider, rather than verified:
1. The comparative advantage of the largest nations is greater than before. The UK stands relatively powerless vis-a-vis the EU, and the EU itself may be dissolving or at least weakening. There is talk of “Nexit” for the Netherlands, yet they are far less well equipped than is the UK to go it alone without the EU. The larger nations have long been a mess, and still are, but the smaller nations cannot coordinate as well as we thought.
2. Brexit is another example of the 1990s unraveling or being reversed. It is hard to imagine that Brexit would have succeeded against the EU of 1985, which among other things still had border checks, Benelux aside. So when exactly did the EU “grow too big for its britches,” at least from an English point of view? I believe this has to be dated back to the 1990s, under Tony Blair, with a second episode coming after the boost in Eastern European migration after 2004, but the liberation of the east was ultimately a 1990s phenomenon as well.
3. Perhaps the law is so complicated, and politics now so dysfunctional, that contemporary governments just can’t handle crises any more. Arguably the USA and UK governments spent their political capital during the financial crisis of 2008 (“trust us on these bailouts”), and they just don’t have enough left in the trust bank. Thus we observe a near-complete paralysis of the British government, with even — especially — the opposition in complete disarray. The existence of party discipline often feels fruitful, but it also means the lack of party discipline can lead to a crisis too readily, unlike in the United States, where there is sometimes party unity but rarely much party discipline.
4. More generally, might the Parliamentary system be worse than many people think? I’ve seen it praised so many times in the blogosphere for its clean, swift, up or down properties. But when there is a leadership void, it hits the legislative and executive branches together, and either before or after the void it is possible to shift very badly off course very rapidly. There are fewer intermediate institutions or checks and balances to set things right, and as Martin Wolf noted: “36 per cent of eligible voters have been allowed to decide “without any appropriate checks and balances””. The suddenness of the Brexit problems could not happen easily in the United States, and along a number of fronts the American system of government is looking pretty good these days. For now. So many trials of endurance!
We’ll see, but those are at least worth a ponder.