It was most visible in territories where the Polish language or culture was dominant or where their adoption could result in increased prestige or social status, as was the case with the nobilities of Ruthenia and Lithuania.

Such a view is widely considered applicable to the population of the Grand Duchy of Lithuania in the times of the Polish–Lithuanian Commonwealth (1569–1795), when the Ruthenian and Lithuanian upper classes were drawn towards Westernization with the adoption of Polish culture and the political and financial benefits of such a transition, as well as, sometimes, with the administrative pressure exerted on their own cultural institutions, primarily the Orthodox Church and Protestant by conversion to the Roman Catholic faith was often the single most important part of the process.

In a letter to the German Franciscans, Grand Duke Gediminas asked them to send monks who spoke Samogitian, Ruthenian or Polish.

[13] When in 1697 the Sejm of the Commonwealth passed a resolution to replace Ruthenian language by Polish in all official actions, it only approved the long-standing status quo.

[14] In addition to Polish, Latin was also used in the documents of the Lithuanian chancellery referring to the Catholic Church, cities under Magdeburg Law, Livonia and foreigners.

[25] From the time of Zygmunt August, correspondence with the Lithuanian elite was conducted almost exclusively in Polish,[25] since the knowledge of Latin in Lithuania was too weak.

[26] In the 1569 Union of Lublin, the Ukrainian territories controlled by the Grand Duchy of Lithuania were transferred to the Crown of the Kingdom of Poland,[27] and thus found themselves under the direct influence of the Polish culture and language.

Ukrainian lands of Kyiv and Braclav voivodeship were rather sparsely populated and attracted a lot of settlers, mostly from Volhynia, but also from central Poland.

Even for those who remained faithful to the Orthodox Church and Ruthenian language, Polish political identity became very important, as they were inspiring to be part of szlachta – a ruling, privileged elite.

[30] The creation of the Greek Catholic Church, following the 1596 Union of Brest which sought to break the relations between Orthodox clergy in the Commonwealth and the Patriarchate in Moscow, put the Ruthenian people under stronger influence of Polish culture.

[34] Some Ruthenian magnates like Sanguszko, Wiśniowiecki and Kisiel, resisted the cultural Polonization for several generations, with the Ostrogski family being one of the most prominent examples.

Remaining generally loyal to the Polish state, the magnates, like Ostrogskis, stood by the religion of their forefathers, and supported the Orthodox Church generously by opening schools, printing books in Ruthenian language (the first four printed Cyrillic books in the world were published in Cracow, in 1491[35]) and giving generously to the Orthodox churches' construction.

Great Prussian families Polonized their names: the Baysen to Bażyński; the Zehmen to Cema; the Dameraw to Działyński, and the Mortangen to Mortęski, the Kleinfelds to Krupocki.

the biggest successes in Polonization of the non-Polish lands of former Commonwealth were achieved after the Partitions, in times of persecution of Polishness (noted by Leon Wasilewski) (1917[41]), Mitrofan Dovnar-Zapolsky (1926[42]).

Dovnar-Zapolsky notes[48] that the Polonization actually intensified under the liberal rule[citation needed] of Alexander I, particularly due to the efforts of Polish intellectuals who led the Vilnius University which was organized in 1802–1803 from the Academy in Vilna (Schola Princeps Vilnensis), vastly expanded and given the highest Imperial status under the new name Vilna Imperial University (Imperatoria Universitas Vilnensis).

[49] By the Emperor's order, the Vilna education district overseen by Adam Czartoryski, a personal friend of Alexander, was greatly expanded to include the vast territories in the West of the Russian Empire stretching to Kiev in south-east and much of the Polish territory and the development of the university, which had no rival in the whole district, received the highest priority of the Imperial authorities which granted it significant freedom and autonomy.

[53] Any Polonization of the east and west territories (Russian and German partitions) occurred in the situation were Poles had steadily diminishing influence on the government.

Inhabitants of a significant part of the Vilnius region used a variant of the Belarusian language, which was influenced mainly by Polish, but also by Lithuanian, Russian and Jewish.

The knowledge of Slavonic intedialect made it easier for Lithuanians to communicate with their Slavic neighbors, who spoke Polish, Russian, or Belarusian.

This gradually limited the use of simple speech to everyday life situations, and gave rise to a sense of contempt for it and Belarusian as the language of work, cursing, but also more emotional and impetuous.

It is difficult to determine a definite number because for the most part, they did not have an established sense of their national identity; they described their language as "Tutejszy" "simple speech" (Polish: mowa prosta) or "Poleshuk" (in Polesia).

In 1924, the Law on Minority Education led to the closure of a huge part of the approximately 350[73] (or 514[74]) existing Belarusian schools, opened mostly during the German occupation.

[81] In the spring of 1922, several thousands Belarusian partisans issued a demand to the Polish government to stop the violence, to liberate political prisoners and to grant autonomy to West Belarus.

That's why the Polish policy in Ukraine initially aimed at keeping Greek Catholic Galicians from further influencing Orthodox Volhynians by drawing the so-called "Sokalski line".

[93] Such actions were condemned by the head of the Ukrainian Greek Catholic Church, metropolitan Andrei Sheptytsky, who claimed that these acts would "destroy in the souls of our non-united Orthodox brothers the very thought of any possible reunion.

The principle of "numerus clausus" had been introduced following which the Ukrainians were discriminated when entering the Lviv University (not more than 15% of the applicants' total number, the Poles enjoying not less than the 50% quota at the same time).

As a consequence of the conflict over the city of Vilnius, and the Polish–Lithuanian War, both governments – in the era of nationalism which was sweeping through Europe – treated their respective minorities harshly.

[citation needed] During Operation Vistula of 1947, the Soviet-controlled Polish communist authorities removed the support base for the still active in that area Ukrainian Insurgent Army by forcibly resettling about 141,000 civilians residing around Bieszczady and Low Beskids to northern areas of the so-called Recovered Territories awarded by the Allies to Poland in the post-war settlement.

The farmers received financial help from the Polish government and took over homes and farms left behind by the displaced Germans, in most cases improving their living conditions due to the increased size of the newly reassigned properties, brick buildings, and running water.

[102] Dr Zbigniew Palski from IPN explains that an identical operation was performed in Ukraine by the Ukrainian Soviet Socialist Republic at exactly the same time.