The Russians were always like that. I recommend you

to read pre-WW2 history as well to find out more. Winter war/Continuation war; conquest of Poland in 1939; Invasion and annexation of Baltic countries; Plots against China over Mongolian issues, and so on.

Stalin was an evil greedy tyrant who wanted to conquer the whole world if not exaggerated. I heard a story saying that Lenin was going to abolish all unfair treaties (Czar) signed with Qing government, which means possible return of lost lands to China from the Russian control. Lenin, however, died before he could do that. Then Stalin came to power and refused to do so. Is it true?