going all the way back

. . . to Western European Germanic culture disparagement of Eastern Slavic culture . . .

racism
resentment
tensions

historical invasions of the East from the West
Napoleon 19th century
Germany 20th century

Russian fear, mistrust
desire for a buffer
forcing the countries between Germany and Russia to be a buffer zone
the resentment of the Russians
the desire to be in NATO

the discomfort of Russia as NATO expanded eastward
the arrogance of The Hegemon to pay no heed

Angela Merkel warned against threatening Russia with Ukraine inclusion in NATO
warned against Western political encroachment into Ukraine

Russia resented Gorbachev letting Ukraine keep Russian territory
Russia resented the disdain and lack of consideration on the part of The Hegemon
Russia seething
Russia takes Crimea
Russia denied Ukrainian neutrality
Russia invades to neutralize Ukraine