Speaking of things people pretend not to exist, Russian historiography frames WWII as lasting from 1941 to 1945. The USSR conspired with the Nazis to divide Europe[1], invaded Poland from the east in cooperation with Germany[2], held a joint victory parade when Soviet and German forces met[3], murdered the Polish people in an industrial manner[4], and so forth. Later, it pretended that the war began only in 1941 and that none of this had happened. These events were officially acknowledged only in the early 1990s, in the final days of the USSR.
And these were only the opening months of the war. Here is Soviet officer Leonid Rabichev giving a chilling description of the final months of the war in Prussia and the extent of Soviet atrocities against civilians: https://www.youtube.com/watch?v=5Ywe5pFT928
Stories like these are why the phrase "Soviet liberators" is used only sarcastically in Eastern Europe.
[1] https://en.wikipedia.org/wiki/Molotov%E2%80%93Ribbentrop_Pac...
[2] https://en.wikipedia.org/wiki/Soviet_invasion_of_Poland
[3] https://en.wikipedia.org/wiki/German%E2%80%93Soviet_military...