Why Russia Is So Upset About Finland and Sweden Joining NATO

 I was watching this video discussion of the likely application of Finland and Sweden to NATO:

I see both short-term and long-term reasons for Russian saber-rattling on this.  Long-term, Sweden and Finland have formidable militaries.  Finland, until the Russian Revolution, was part of the Russian Empire. In Putin's weird amalgamation of recreating the Russian Empire and the Soviet Union, as demonstrated by raising the hammer and sickle flag over Melitopol, conquering Finland is likely among his long-term goals.

Short-term, Putin's threats reflect that what will Russia do?  They are not going to invade Finland.   He can mass Russian troops and tanks along the Finnish border.  Russia is failing to conquer a third-rate (in everyone's eyes on February 24th) military.  Russia would have to move troops and tanks from...where?  Tanks and soldiers threatening Finland are not available to conquer Ukraine, which is already a nearly lost cause. 

Could Belarus or Kalingrad be the source of an opening battle?  My impression is President Lukashenko's mini-me control of Belarus is shakier than Putin's control of Russia.  I suspect he knows that conventional war against an Article V nation would have a Polish flag flying over Minsk in short order.  It is 346 miles from Warsaw to Minsk and Warsaw is quite some distance from the border.

Kaliningrad?  Surrounded by Poland and Lithuania, it would like fall rapidly.  Putin might decide this existential threat to Russia deserves nuclear war.  This would likely destroy Europe, and cause 200 million dead in the U.S. and Canada (fallout, even if Canada was not directly attacked).  But the highly concentrated Russian population would within a few months be carrion consumed by glowing Russian wolves in St. Petersburg and Moscow.  Russia would be a Radioactive Stone Age for several generations.  His place in Russian history books of the 22nd century , for the perhaps five million remaining Russian-speakers, would be assured.

UPDATE: Belarus is putting its military into exercises towards the Lithuania border, while insisting that they are no threat to any other nation.  Did we not hear that a couple months ago from Russia.