I don't think Russia has forgotten about it and we should assume that they have.
Well, cold war aside. A key to understanding the mentality of Russians is the idea of being invaded. They have never invaded western Europe, except in counterattack to the Nazis. When you talk to them as individuals, they stayed in firm control of eastern europe to guarantee they would prevent any repeats of Europes invasions.
For the 180 years prior, they will point to Europe and Germany invading them with Napoleon, and Moscow burning before they fled that winter.
Next the horrifyingly bloody Anglo/French invasion of Crimea that had no sane cause. The British simply didnt like eastern orthodox (locals) in control of Turkey.
Next again, the Germans invaded deeply into Russia during WWI. (the misery created by that war unleashed the communist revolt, heavily encouraged by Germany to take russia out of the war)
Then last, Hitler and the Nazis invaded and tens of millions died.
So ok, communism aside (which while they are *fine* with hard nationalist strongmen, you are hard pressed to find a Russian who wants communists back in charge)
But communism aside, say you are a Russian, it’s after WWII. Now you hold Berlin and half of Europe, do you give it back to their control? Or do you say “That was it, Never again!”?
Last, what is your response as a Russian when the Warsaw pact desolves, and you quietly watch as NATO expands right across eastern Europe, into every country surrounding you. Even into Stalin’ home in Georgia. Georgia fell at the hands of a euro financier,,Soros. And this Soros brought the Ruble to its knees by shorting it, crashing it, then demanding it float and NOT be tied to the dollar. This brought a decade of depression as bad as the Soviet times to Russia.
And as you look at the EU, you see they are hungry to control your oil and gas, its delivery routes, and its prices, and are doing so through Yukos.
You watch, incredulous at American criticism for you fighting Osama’s boys in Chechnya, and the Ossetians who murdered those school kids in Beslan. After all, after 9/11 you gave them immediate use of a former Soviet Air Force base to attack Afghanistan.
If you were a Russian, and you saw all this, you would say, “Here we go again”. And that is why Putin is behaving the way he is.