Well, start with Putin's 2005 address to the Russian nation
"Above all, we should acknowledge that the collapse of the Soviet Union was a major geopolitical disaster of the century. As for the Russian nation, it became a genuine drama. Tens of millions of our co-citizens and compatriots found themselves outside Russian territory. Moreover, the epidemic of disintegration infected Russia itself."
Every analyst of current Kremlin policy starts from there, and the restoration of the USSR as being Putin's personal crusade and the keystone of his foreign policy. He has already invaded and subjugated independent Georgia, then Crimea, then eastern Ukraine (Donbas) before the March invasion. The Baltic states have invited NATO forces in continually in recent years for assistance and training and other support in recent years, and not because they're afraid of a renewed invasion by Germany, or even Poland. It's propaganda bull that Crimea is part of greater Russia and happily left Ukraine to return to Mother Russia in 2014 is it? You apparently discount the BBC, your own media and think tanks, so who do believe?
Once he has the USSR back (as if!) he'd be looking over the Finnish border just as his Soviet predecessors did. Finland proved a very hard nut to crack in 39/40, and its efficient in-house military preparedness post '45 allied to its natural geographic defensive advantages are what that has kept that country free.
