Arguing NATO didn't expand into the Baltic states is semantics, at best. Sure the countries have to apply to join but the current NATO members have to acquiesce. Even with this relationship the US can (and has) communicated policy prior to expansion. The act of expnasion itself is evidene of US policy since the US could veto it fif it was something it didn't want.

My suspicion is you're viewing the US as a benign hegemony. The problem with this thinking is it makes it harder to see things from the other side, namely that another foreign power might reasonably perceive "benign" actions as hotile.

This is especially true of NATO, which was founded on the idea of screwing the USSR (quite literally). Well the USSR doesn't exist anymore yet NATO persists. Russia has to view that as aggressive especially with continued expansion. The standard response here is that NATO is a defensive alliance, which is complete BS (eg Libya, Kosovo, basing nuclear weapons capable of hitting Moscow in Turkey).

> Why do you think that these sovereign European nations actually want to be a "buffer"?

Because there are advantages to being neutral. You can't get roped into a war you didn't consent to. The great powers that border you tend to be happier with your neutrality than picking sides. Finland, Sweden, Switzerland and Ireland are all countries in Europe who have policies of neutrality. A neutral state between great powers is by definition a buffer state.

And like I said, the US does exactly the same thing. Do you think the US would idly sit by if Mexico and Canada decided to join a military alliance with China and allow China to build forward operating bases along the US border? There's absolutely no shot.

So why if the US would never allow Chinese military bases on its border should the US be surprised that Russia would have the exact same objection?

> Why do you think somebody should have a right to constrain their sovereignty?

Because joining NATO requires mutual consent. No country has a right to join if NATO declines and NATO does have a right to decline. Germany in particular has indicated they had no intention of allowing Ukraine to join NATO for pretty much exactly the reasons we're seeing now.

> With Finland joining NATO, Russia will now have 1340 km border with NATO. What Putin is going to do about that?

That's my point: this has been a massive miscalculation by Putin. But not all borders are created equal. Geography matters. A border with Ukraine is of more strategic threat than a border with Finland just because most of Ukraine is flat.

> This is precisely what they tried to do with this invasion

My sense is they trid to decapitate Ukraine's leadership and pave the way for a pro-Russian regime. This was a massive miscalculation. TListen to anyone who knows anything about the military and you'll find estimates that Russia would probably need over 400,000 soldiers to occupy Ukraine. They don't have that. They couldn't afford it if they did.