俄罗斯人在乌克兰正是历史上的殖民，assimilation造成出的。还有一部分是苏联时期跑去占领的。

In general the population of ethnic Russians in Ukraine increased due to assimilation and in-migration (colonization) between 1897 and 1939 despite the famine war and Revolution. ... Finally some of those who were counted as Russians in Soviet times declared themselves Ukrainian during the last census.