I wrote that some years AFTER the nobility was polonised, the masses did so as well. Of course, Polish people colonised these areas.
Russians had their interest in lowering Polish population. After the Napoleonic Wars they promised to give as so called "Ziemie Zabrane" (Western Krai in English, and in Russian nomenclature) containing of non-Polish territories like Minsk or Vitebsk, but of places like Grodno, Vilnius and Bialystok as well. They had their interest in lowering Polish population there because it would be a good excuse why they don't attack these lands to Congress Poland.
So surely, I wouldn't call them THIRD PARTY
I thing thah in this period, the Russian Empire is the victorious party, not Poles, nor are Lithuanians, Belarussians or Ukrainians
Another thing- I am a slavophile and russophile, so I hope that nobody will charge me of russophobia because I don't trust the Tsarist censuses