50 years by USSR + ~100 years by Russian Empire[0]
"integration efforts haven't really that "huge"."
Mass deportations[1] (5% of the population, most of whom died during severe Siberian winters), total ban of press and schools in local language[2][3], oppressive state police to prosecute or silently get rid of anybody standing against occupant government[4]. In my dictionary, that amounts to "huge" easily.