> geographical vulnerability of Russia's western border
This is Russia's argument, but it is nonsense. Nobody would attack any Russian border, western or otherwise, because Russia has thousands of nuclear weapons. It's as simple as that.
Nuclear weapons prevent an all-out invasion, but they're not much good at anything else. The US, for example, could not have used nuclear weapons in Afghanistan or Iraq.
The US is something of an outlier. Most countries maintain much smaller militaries. They have them on hand for a variety of purposes: disasters, foreign peacekeeping, border patrol, and keeping their hand in Just In Case.
NATO countries, for example, are supposed to keep militaries so that Russia doesn't get any ideas. Say, Wagner troops meander across the border into Poland. Russia clutches its pearls and says, "Oh, no, don't end the entire world by nuking us even though it's obvious that we ordered it." So troops would get sent... which is why it never actually happens.
How much military you need to achieve that is up for debate. The US often claims that other NATO countries need more, and that the European countries are relying on America to provide most of that deterrent. But the US is almost certainly providing way, way, way more deterrent than is needed -- more about national preening than serious consideration of needs.
That was what I was trying to explain. Nukes are a blunt weapon, and they want to have a bit more precision. They're not going to nuke Russia if Wagner group made a little, deniable cross-border excursion.
Nukes get MAD real fast. If their only weapon is a nuke, their bluff could easily be called.
Very few countries spend 4% of GDP on the military, and most of them are at war. Not even the US, which comes in at 3.5%. NATO countries are supposed to spend (IIRC) 2%, but most don't.
It's a 2% that they might like to have back, but militaries are pretty good make-work programs. Even Japan, whose constitution prevents it from having a military, still spends 1% on its military.
Not clear what your point is? Are you saying that indeed there was any chance of Nato invading Russia? I think that was what you're implying, but I'm not sure, since you replied to me with a question.
Do you have any scenario of how that would happen, so that Russia's invasion of Ukraine makes any sense as a preemptive move?
This is Russia's argument, but it is nonsense. Nobody would attack any Russian border, western or otherwise, because Russia has thousands of nuclear weapons. It's as simple as that.