“No, it was Lenin who incorporated these Russian areas into Ukraine. Before that, Tsars incorporated pieces of Poland, Romania, and Hungary into it.”
Incorrect, because none of these areas in Lenin’s time were Russian. Crimea had diverse population with Tartars being the largest group. What is today the Donbass was almost entirely populated by the Don Cossacks.
These groups were wiped out between 1920 and 1944, and it was only after that they were replaced by Russian speakers.
Who were Don Cossaks by ethnicity? Everything you know about Ukrainian history is a lie. Review the forms filled by people from the area who immigrated to the US in the early 1920s. There was no such thing as Ukrainian at the time.