Because the sovereign and independent Eastern European nations wanted to become part of NATO, and NATO tanks didn't need to force itself on a single nation, it was invited( a single country, nor change the borders, unlike Russia's military occupation of portions of Moldova, Georgia and Ukraine.

I'm not sure your average Serb would agree ...

Because when Greece has been recently openly allying itself with Russia, I don't see NATO troops from Italy or Albania or Bulgaria attempting to break apart portions of Greece.

No, they just get the Troika to do it by proxy.

I'll restate what I said before - I'm not defending Putin's regime as such. It's tyrannical and corrupt and no sane person would die defending that hill. Just that Russia's actions are perfectly understandable as defensive and reactive in nature. Yes, the Eastern Euro countries (mostly) joined NATO of their own free will (more accurately, they had little alternative either way with Russia being dead in the water through the 90s). What of it? The fact remains there's an explicitly anti-Russian coalition on Russia's doorstep, and allied groups like the EU pushing into historically-Russian territories. They're understandably afraid of the Germans pushing east of the Vistula - after all, it didn't end well the last two times.

"Rebuilding the Soviet Empire" is exactly the kind of propagandistic slogan that contributes to crises in the first place - viewing your enemy as some kind of inscrutable, uncompromisingly aggressive monster rather than a country concerned for its survival and who possesses few natural defenses.