The fundamental long term (2000s-2100s) challenge to American national security is that North America, which we economically and politically dominate, is quite small in size, population, resources and economics relative to Eurasia.

This is relatively moot while large parts of Eurasia are active military allies of the US or are largely demilitarized and opted out of the great power game (the EU, Japan), an option made possible by US protection. The amount of Eurasia left over once US allies and

(let us speak bluntly) protectorates are subtracted out is a power center whose rivalry the US is able to manage.

This is why US forward deployments and defense commitments are so crucial. It's not that the US has inextricable national security interests in Montenegro, much that

I love them we do not. But that we have national interest in Europe not being subject to power rivalry and competing spheres of influence and all the long term uncertainty that comes with it.

And while it is not the case that if the US retreated to isolationism some new alliance would form tomorrow, the winds change fast. Today all former axis powers are key allies, many former allied powers rivals. What will another 80 years bring?

We learned this threat the hard way, from an axis that very nearly did put together an alliance able to threaten our very home, and again from a globe trotting communism that threatened the same that we barely contained by leaning on our allies.

The exact roles change. East Asia has risen in importance while Europe, mostly no longer frontline, has been able to mostly demilitarize. India will be, if we play our cards right, a key ally of the future. But the core structure we built against the nazis and communism remains

sound. We stay safe by maintaining enough global dominance - and by protecting enough peaceful parts of the globe, that our enemies can be capped at regional rival, not regional hegemon or global rival. We stray from that at peril, likely not in the next decades, but in time.

@ClaireBerlinski did a great thread making a similar argument a year or two ago that's well worth reading but that I've lost to the tides of "before I was on twitter."