The term Kresy, meaning "Outskirts" or "Borderlands", was first used to define the Polish eastern frontier. The term referred to the eastern frontiers of the Polish-Lithuanian Commonwealth. During the period of the Second Polish Republic, the Borderlands roughly equated with the lands to the east of Curzon line. In September 1939 the Soviet Union annexed the Borderlands and incorporated them into the Soviet republics of Ukraine, Belarus and Lithuania. When the Soviet Union broke up, these territories remained part of those respective republics after they gained independence.
According to the Dictionary of the Polish Language (1807) by Samuel Bogumil Linde, Kresy referred to the Polish eastern frontier. The Tatar Horde settled on the Lower Dnieper River in the Borderlands. For the first time in literature, this term was probably used by Wincenty Pol in his poems entitled “Mohort” from 1854 and in “Pieśń o ziemi naszej”. Pol claimed that it was the line from Dniester to Dnieper River so the land of Tatar borderland. At the beginning of the 20th century the meaning of the term Borderlands expanded to include the lands of the former eastern provinces of the Polish-Lithuanian Commonwealth, to the east of Lwów-Wilno line, and in the period of the Second Polish Republic the Borderlands were equated with the land to the east of Curzon line. Currently the term Eastern Borderlands describes former, eastern lands of the Second Polish Republic (1918-1939).
Between the 16th and 18th centuries, the Eastern Borderlands were situated on the lower Dnieper River under so-called ‘porohy’ in the then Kijov province. After the Union of Lublin of 1569 the "Wild Fields" were incorporated into the boundaries of the Republic of the Two Nations. At this time these areas were thought to have been uninhabited.
1772 marked the beginning of the partition of theRepublic (Res publica) of the Two Nations. This process took place in three stages (annexations). In the first partition (1772) the tsarist Russian Empire annexed Polish Inflanty, the northern part of Polotsk province, Vitebsk province, Mscislaw province and the southeast part of Minsk province (about 92 thousand km², 1,3 million people). Austria annexed entire Galicia, certain regions near Zamosc and northern Lesser Poland (about 83 thousand km² and 2,65 million people). During the second partition in 1793 Russia took Belarusian and Ukrainian lands to the east of Druja-Pinsk-Zbrucz line, concretely: Kiev, Bratslav, part of Podolia, east part of Volhynia and Brest, Minsk and part of Vilnius (Polish: Wilno) (about 250 thousand km²) provinces. The third partition took place in 1795 and Lithuanian, Belarusian and Ukrainian areas to the east of the Bug River and Niemirow-Grodno line (about 120 thousand km²) were occupied.This period in the history of Poland, especially in its eastern part, was a period of frequent national rebellions (November Uprising, January Uprising), persecutions, forced resettlement and penal deportations to Siberia and denationalization of Poles. The eastern borderlands of Poland historically belonged to the last regions in Europe where serfdom was abolished: In 1848 it was eliminated in the Austrian partition and in 1861 in the Russian partition.
March 1919 was especially turbulent for the Eastern Borderlands of Poland, as it was the time of the rebirth of the Polish state and the formation of the border. At that time, Poland was involved in three wars for its Eastern borders: with Ukraine, Soviet Russia, and Lithuania. As a result, Poland annexed territories that were previously under Russian administration situated to the east of the Curzon line. This terrain later formed the Eastern provinces of the Second Republic of Poland: eastern part of Lwów Voivodeship, Nowogrodek Voivideship, Polesie Voivodeship, Stanis%C5%82aw%C3%B3w Voivodeship, Tarnopol Voivodeship, Wilno Voivideship, Volhynia Voivideship and eastern part of Białystok Voivideship.
The population of the Kresy was multi-ethnic primarily made up of Poles, Ukrainian and Belarusian. In total, ethnic Poles were the largest ethnic group in these regions, and were demographically the largest ethnic group in the region's cities. Other national minorities included the Lithuanians (in the north), Jews (scattered in cities and towns across the area), Czechs (in Volhynia), and also Russians.
Mother language given in 1931 Polish census was following:
In 1931, according to the National Census, the largest cities in Polish Eastern Borderlands Voivodeships were:
As a consequence of the Molotov-Ribbentrop pact, on September 17, 1939 the territory was annexed by the Soviet Union, and a significant part of the ethnic Polish population of the eastern Kresy was deported to other areas of the Soviet Union including Siberia and Kazakhstan.
When Nazi Germany and Soviet Union signed the Non-aggression treaty on 23rd of August 1939 in Moscow, it included a secret protocol regulating the course of the demarcation line between Germany and the Soviet Union. The Soviet Union invaded Poland on the 17th of September moving fast to the Western border. Already on the 22nd of September both aggressors celebrated the success of their armies in a joint parade of victory in Brest-Litovsk (today's Brest). In the end the course of the border was designated by the agreement on borders and friendship between the Third Reich and the Soviet Union signed on the 28th of September. Simultaneously Communist governments for Western Ukraine and Western Belarus were formed and announced their intention on joining the respective republics in the Soviet Union. Polish command and government were completely surprised by the Soviet attack and for three months, until the 18th of December, they could not announce that Poland was in a state of war with the USSR or even give clear orders to their soldiers.
After the German invasion of the USSR which took place the 22nd of June 1941, the Germans moved approximately a thousand kilometers eastwards in the first weeks, breaking apart or taking Soviet troops into capture. Afterwards part of the territory was included in the Greater Germany, whilst the rest was passed to the Reichskommisariats.
In January 1944, Soviet troops reached the former Polish-Soviet border (by September the 17th 1939), whereas till the end of July they again brought under control the whole territory that was granted to the USSR with the German-Soviet Boundary and Friendship Treaty of 28 September 1939, which are currently the terrains eastward from the Eastern Polish border.
Already during the Teheran Conference in 1943, a new Eastern Polish border was established, in effect sanctioning the Soviet territorial acquisitions from September 1939 and ignoring protests from the Polish emigre government in London.
The Potsdam Conference gave consent to the deportation of the Polish people from the former eastern Polish borderlands, but the issue with the Polish western border was still unsolved. The Allies decided to hand to Poland the pre-1937 officially recognized territories of Germany situated east of the Oder and the Lusatian Neisse River, east of this so-called Oder-Neisse line (excluding the northern part of former East Prussia, which became part of Russia as Kaliningrad Oblast) during the period of the temporary Polish jurisdiction and up to the moment, where territorial borders were finally acknowledged by the peace treaty.
After the Second World War, the Polish eastern lands were incorporated into Soviet Union as part of the republics of Ukraine SSR, Belarus SSR and Lithuanian SSR. The annexation of these territories was celebrated in the former Soviet Union and is also currently celebrated in independent Belarus as the “unification of Belarus”.
The official name of the attack on Poland in 1939 had been the Liberation Conquest of Western Ukraine and Western Belarus in the Soviet Union. After the collapse of the Soviet Union, these territories formed the independent republics of Ukraine, Belarus and Lithuania; they retained their inter-republic and 1945 borders to Poland.