Vladimir Putin is restoring the tsarist empire, in good part because Kievan Rus was the source of Muscovite Rus.  The Russian Orthodox Church traces its history to Kiev.  The Russian and Ukrainian languages are very similar, and of course the opening to the Black Sea has been a historic aim.

All the old Soviet colonies are trembling in their boots, because they study Moscow like the historic enemy it is.

Yes, Putin felt pushed by NATO, but NATO was pushed by the fears of the Poles, Hungarians, Swedes, Finns, etc., etc.  They had endless debates within NATO.  It is quite possible that they pushed too hard, but it's not totally irrational if you were victimized by Russia within living memory.

Putin's ambitions are not rational in a narrow sense; they are messianic.  This is nuts, but I keep studying Russia and the rest (and listening to Stephen Kotkin), and I believe my interpretation is correct.

Putin addresses the nation following the Wagner group's move toward Moscow.
The flag on the right of the picture superimposes the imperial standard of the tsar over the tricolor of Russia.

The Germans are the only ones who are not talking about it in public.  Putin is a wounded soul, in many ways, but so were many of the aggressive tsars.  And Xi Jinping. 

Many major wars have that psychological trigger.  The "century of humiliation" is a nutty idea because it throws the Brits and Americans into the same bag as the Rape of Nanking.  That's historically bizarre, but that is what they are teaching their soldiers and young people.