In Late Middle Ages, following the extinction of the Rurik dynasty in 1323, the Kingdom of Poland extended east in 1340 to include the lands of Przemyśl and in 1366, Kamianets-Podilskyi (Kamieniec Podolski).

The settlement of Poles became common there after the Polish–Lithuanian peace treaty signed in 1366 between Casimir III the Great of Poland, and Liubartas of Lithuania.

According to the Nestor – Primary Chronicle tribe of Lendians were 'Lachy' (Lechites) and their Duke Wlodzislav took part in dealing with Byzantine empire together with the Rus.

[8] It is first attested in AD 981, when Vladimir the Great of Kievan Rus conquered the Red Ruthenian strongholds in his military campaign on the border with the land of Lendians.

During this time Polish settlers helped to economically develop the region and they formed a significant element in the courts of the Galician rulers.

[11][12] Following the extinction of the Rurikid dynasty and the end of the Galician-Volhynian kingdom, this region was seized by the Polish Crown, and included in the Polish–Lithuanian peace treaty signed in 1366 by Casimir III of Poland, with Liubartas of Lithuania.

[11] Polish rule involved expansion of Jesuit schools and large scale construction or ornate castles and estates that included libraries, art collections and archives that in many cases were the equal in importance to those in Poland itself.

[11] Also Polish Kings Michał Korybut Wiśniowiecki, John III Sobieski and Stanisław Leszczyński were born in present-day Western Ukraine.

Following the successful uprising of Bohdan Khmelnytsky against the Polish crown in the mid 17th century, Ukrainian lands east of the Dnipro River, the Cossack Hetmanate, became briefly independent and then became an autonomous part of Russia.

[11] By the late 18th century, approximately 240,000 people of the Volhynian, Podilian and Kyiv regions, or 11% of the population, were Roman Catholics, most of whom were Poles.

[11] In the mid seventeenth century the Cossack Hetmanate east of the Dnipro River successfully rebelled against the Polish-Lithuanian Commonwealth, and after a brief period of independence became an autonomous area under the Russian Empire.

In this region some Poles and Polonized Ukrainian nobles who had joined the Cossacks remained and in some cases even obtained high positions in the local administration.

The Hetmanate's most prominent schools, the Kyiv Academy and Chernihiv Collegium, used Polish and Latin as languages of instruction.

[16] Poles included wealthy magnates with large estates, poorer nobles who worked as administrators or soldiers, and peasants.

Long after this region ceased being a part of Poland, Poles continued to play an important role in both the province and in the city of Kyiv.

Polish landlords owned approximately 46 percent of all private property in Ukraine west of the Dnipro River.

[18] Henryk Józewski, a Pole from Kyiv, served in the government of the Ukrainian People's Republic under his friend Symon Petliura and later as governor of Volhynia under Poland.

The wealthy magnates tended to oppose the Polish insurrections, identified with their Russian landlord peers, and often moved to St. Petersburg.

[11] As a result of an anti-Russian insurrection in 1830, the Polish middle and poorer nobility were stripped of their legal noble status by the Russian government.

Due to assimilation, whereas at the time of the annexation of Ukrainian lands by Russia in 1795 10% of the population were Poles,[16] in spite of ongoing migration of Poles from central Poland into Ukrainian lands,[11] by the end of the nineteenth century only three percent of the total population of these territories reported that Polish was their first language.

As a result of such policies, despite larger Ukrainian family sizes the percentage of the population who were ethnic Poles grew significantly, to over 25% by 1910.

[11] The advance of the Bolshevik armies, the Polish–Soviet War of 1919–1921, and the incorporation of these Ukrainian lands into the USSR, led to a massive exodus of Poles, particularly landowners and intelligentsia, from Ukraine into Poland.

The rest of the territory would be captured during an offensive of the Polish–Ukrainian War by the Polish Armed Forces entering these lands from Poland, in July 1919.