When a country looses it's national identity, then, yes, it is in decline.
I'm personally horrified by Trump's xenophobia and racism, but the fact is burning people's stuff and flying foreign flags and beating up police officers just plays right into his hands.
If you like that place so much, go back there. My dad was an immigrant from Germany. You'd never see me waving a German flag. My wife is an immigrant from China. You won't see her waving a commie Chinese flag, either.
Who is threatening who? NATO promised not to expand in the 1990s, but now we've moved up right to Russia's borders in former Soviet Republics.
Okay, let's look at that one.
Tibet was never recognized as an independent country. It was always seen as a part of first the Qing Dynasty, then the Republic of China, before the People's Republic reasserted its authority there.
The problem with our dealings with China is that we keep playing these games with them that their country isn't their country. Taiwan, Hong Kong, Tibet, Xinjiang, even some stupid islands in the South China Sea.
I wouldn't go that far, because Russia initially agreed to the separation. But an adjustment of borders based on demography isn't really an unreasonable ask.
There's no way Ukraine is going back to their 2014 borders. It just isn't happening.