> Again, apologies if I sound obtuse.
You're not, I was thinking of how to reconcile the two comments while writing the second one actually. I see globalization as driven by a) inevitable and b) irreversible trends. Like increasing ease of movement, ease of communication, ease of money transfer (Bitcoin). That doesn't exclude decentralization.
For your first point:
"Decentralization" doesn't necessarily entail every country breaking up into a billion tiny Singapores. It just means decisions being made locally, from the bottom up. In the US, it could look like increased states rights. Want to try libertarianism? Want more refugees? Legal drugs? Go ahead. There wouldn't be half the hysteria if willing states could just opt out of welcoming refugees. They'd keep them out, but that would be that, and there wouldn't be much fuss beyond that. The attitude on the right just would be: "glad we avoided that, why go through the trouble?", instead of moral outrage and self-preservation instincts. In complex governmental systems, you inevitably have coercion, which leads to instability.
Someone in the Northern UK might not meet many immigrants, but he doesn't like the idea of someone from migrant-heavy London voting to bring migrants into his little town, if he views it as a threat. It breeds resentment. Democracies, especially complex ones, have to compromise between millions of voters that each want different things. The more people that want different things from official government policy, the more unrest. If you're in a political minority, there's functionally no difference between a government being democratically elected by a majority that is nothing like you, and an authoritarian regime that's accountable to nobody. In both cases, you're (effectively) not represented (how many Clinton supporters feel represented by Trump?). The larger the scale, the more disparate the population, the more important it is to favor local power structures over national ones.
You know the argument that goes "democracy is just war by another name", and is a very nice thing because it allows for "bloodless revolutions"? That's not the case if the country is too complex (population too disparate) and the government represents only 30% of the country rather than 80% (pretty sure only a quarter of the country voted for Trump, the earlier figure is a reference to that, everyone else probably dislikes him to some extent; and in a functional, ideal country, you may not have voted for the current government, but still don't mind them too much, that's what the 80% refers to).
Not sure you mean by "how we got here". Low growth and economic uncertainty seem necessary for populism. In the EU, the euro is the main cause of that (not an optimal currency area, preventing there from being true freedom of movement for labor, as well as messing up the exchange rates and screwing any country that isn't Germany). I'm very pro-EU (and live there) but there's little doubt in my mind that the euro is responsible for much of the rise in populism here, and it's the quintessential example of something done for small incremental efficiency gains while disregarding the systemic aspects. The Greece situation is already worse than the US Great Depression, and resembles the one between creditors and Germany before WW2. It isn't that bad yet, but the only reason is that they had the euro, so inflation and capital flight couldn't destroy the value of their currency. Yet, in all of history, every multinational currency has eventually collapsed. Greece may not have the euro forever. The current debt loads aren't the only problem: if any country leaves, the destruction of wealth caused by inability to settle TARGET-2 balances might cause a cataclysm. In other words, we increased systemic complexity, and vastly increased systemic risk.
For your second point: you can coordinate to solve global problems, without increasing systemic complexity and risk. In a more decentralized world, you'd have more direct governments, and so populations that really care about "green" would just vote straight for that, and those that don't would eventually have enough smog that they would vote straight for it, too. Right now you have 50+% of the US population that wish US climate policy was more progressive but has exactly 0% of power over those policies. Wouldn't decentralization be better on the whole?