At the end. U.S.S.R was on the side of Germany for years during WW2. [1,2]

After all, they enjoyed invading Poland with Germany, massacring quite a few Polish folks. [3,4]

[1] https://en.wikipedia.org/wiki/Germany%E2%80%93Soviet_Union_r... [2] https://en.wikipedia.org/wiki/Molotov%E2%80%93Ribbentrop_Pac... [3] https://en.wikipedia.org/wiki/Vasili_Blokhin [4] https://en.wikipedia.org/wiki/Soviet_invasion_of_Poland