"With the rise of industrialisation, many Russian skilled workers and engineers arrived in the region. The Donbas was very strongly Russified in the 1930s." In 1991, however, 83% of the population of the Donbas region voted in favour of Ukrainian independence."
https://www.france24.com/en/europe/20240408-ukraine-donbas-ten-years-of-war-russification-russia-donetsk-luhansk