Joachim asks a good question in the comments -

I’d be interested in an expanded version of your thoughts on nationalism. My perspective is quite different – global problems require global solutions – but then you’re from the “USA! USA!” while my continent has been devastated by two world wars (more recently, consider e.g. the troubles in Yugoslavia.)

I think nationalism is like a catalyst or accelerator - it makes a place go more in the direction it's currently going. During a renaissance, nationalism makes more people excited to try new things, explore, invent, and expand. During a recovery period, nationalism encourages solidarity, a helping hand, and backing each other up instead of just feeling defeated.

It cuts both ways - in a beaten down, embarrassed nation that's paying reparations to the other side, nationalism really makes that anger and hostility get explosive - that's what Hitler whipped up. On the other hand, nationalism among the allies helped them carry on strongly, survive, and triumph. Keep calm and carry on...

Nationalism in North Korea translates to more loyalty to the insane regime, whereas nationalism in South Korea means hard work, modernization, and a high quality of life.

Anti-nationalistic countries tend to meltdown and self destruct, like England backing down during the Suez Crisis. Birthrates fall, the economy grows slower or contracts, and the country falls into disrepair and ruin.

A nationalistic pride really spurs whatever the current sentiment is forwards and makes more of it. During a golden age, it makes the nation's culture really flourish and expand rapidly, having the art, craft, technology, and spirit of the nation grow rapidly. Nationalism + hatred is an incredibly bad thing, but that's not the fault of nationalism: It's the fault of hatred. Hatred is also bad in anti-nationalistic places, though it tends to display itself in those places more as self-loathing and passive aggression and inward-directed destruction.

An interesting question is what's better in a fundamentally flawed place - nationalism or no nationalism? I don't think there's a great answer to that... if you had some power in one of those places, you'd want to fix the fundamental flaws first and foremost.

Then, in a nation that's really flourishing, cultivating a spirit of pride and celebration in the nation's achievements tend to accelerate progress.