military plan
A military operation plan (commonly called a war plan before World War II) is a formal plan for military armed forces, their military organizations and units to conduct operations, as drawn up by commanders within the combat operations process ...
that was created in the 1920s and the 1930s in case of war against the
Soviet Union
The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
. Unlike
Plan West
Plan West () was a military plan of the Polish Army of the Second Polish Republic, for defence against invasion from Nazi Germany. It was designed in the late 1930s.
Background
While Józef Piłsudski was the dictator of Poland, planning concent ...
(''Plan Zachód''), it was being prepared during the whole
interwar period
In the history of the 20th century, the interwar period, also known as the interbellum (), lasted from 11 November 1918 to 1 September 1939 (20 years, 9 months, 21 days) – from the end of World War I (WWI) to the beginning of World War II ( ...
, as the government of the
Second Polish Republic
The Second Polish Republic, at the time officially known as the Republic of Poland, was a country in Central and Eastern Europe that existed between 7 October 1918 and 6 October 1939. The state was established in the final stage of World War I ...
treated the Soviet Union as the greatest potential military threat that was capable of initiating a full-scale war. However, only a few loose historical documents remain of the original plan today.
Background
Since its establishment after
World War I
World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
, the
Second Polish Republic
The Second Polish Republic, at the time officially known as the Republic of Poland, was a country in Central and Eastern Europe that existed between 7 October 1918 and 6 October 1939. The state was established in the final stage of World War I ...
Silesian Uprisings
The Silesian Uprisings (; ; ) were a series of three uprisings from August 1919 to July 1921 in Upper Silesia, which was part of the Weimar Republic at the time. Ethnic Polish and Polish-Silesian insurrectionists, seeking to have the area tran ...
Germany
Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
and the
Soviet Union
The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
.Stanley S. Seidner, ''Marshal Edward Śmigły-Rydz Rydz and the Defense of Poland'', New York, 1978, chs. 1-2.
In the 1920s and the 1930s, Polish leaders focused their efforts on countering the potential threat from the east. Fresh were memories of the Polish-Soviet War and the Battle of Warsaw, which saved Poland and the rest of Europe from the spread of the
Bolshevik Revolution
The October Revolution, also known as the Great October Socialist Revolution (in Soviet historiography), October coup, Bolshevik coup, or Bolshevik revolution, was the second of two revolutions in Russia in 1917. It was led by Vladimir L ...
by force.
According to the British historian
A.J.P. Taylor
Alan John Percivale Taylor (25 March 1906 – 7 September 1990) was an English historian who specialised in 19th- and 20th-century European diplomacy. Both a journalist and a broadcaster, he became well known to millions through his telev ...
, the Polish-Soviet War "largely determined the course of European history for the next twenty years or more.... Unavowedly and almost unconsciously, Soviet leaders abandoned the cause of international revolution". It would be twenty years before the Bolsheviks would send their armies abroad to "make revolution".
Ronald Grigor Suny
Ronald Grigor Suny (born September 25, 1940) is an American-Armenian historian and political scientist. Suny is the William H. Sewell Jr. Distinguished University Professor of History Emeritus at the University of Michigan and served as directo ...
, ''The Soviet Experiment: Russia, the USSR, and the Successor States'', Oxford University Press, Google Print, p.106 /ref>
According to the American sociologist Alexander Gella, "the Polish victory had gained twenty years of independence not only for Poland, but at least for an entire central part of Europe". Aleksander Gella, ''Development of Class Structure in Eastern Europe: Poland and Her Southern Neighbors'', SUNY Press, 1988, Google Print, p. 23 /ref>
Since both the
Polish Army
The Land Forces () are the Army, land forces of the Polish Armed Forces. They currently contain some 110,000 active personnel and form many components of the European Union and NATO deployments around the world. Poland's recorded military histor ...
and the government in
Warsaw
Warsaw, officially the Capital City of Warsaw, is the capital and List of cities and towns in Poland, largest city of Poland. The metropolis stands on the Vistula, River Vistula in east-central Poland. Its population is officially estimated at ...
were certain that war against the Soviets was inevitable, preparations for it were far more advanced than those against Germany. It was only after 1935, when anti-Polish propaganda in Germany increased, that the German threat became visible enough for army planners to begin drawing up Plan West. Even in 1939, the number of completed fortifications in the east of Poland vastly outnumbered those in the west.Stanley S. Seidner, ''Marshal Edward Śmigły-Rydz Rydz and the Defense of Poland'', New York, 1978, pp. 105–106.
Interbellum Polish–Soviet border
Poland's border with the Soviet Union was 1,412 km long. By comparison, the border with Germany, including
East Prussia
East Prussia was a Provinces of Prussia, province of the Kingdom of Prussia from 1772 to 1829 and again from 1878 (with the Kingdom itself being part of the German Empire from 1871); following World War I it formed part of the Weimar Republic's ...
, was more than 20% longer, at 1,912 km. Neither border contained any major geographical obstacles, which made their defence very difficult.
In the north was flat land with huge forests such as Puszcza Nalibocka, the Wilderness of Naliboki. In addition, a major railway connecting
Moscow
Moscow is the Capital city, capital and List of cities and towns in Russia by population, largest city of Russia, standing on the Moskva (river), Moskva River in Central Russia. It has a population estimated at over 13 million residents with ...
to
Western Europe
Western Europe is the western region of Europe. The region's extent varies depending on context.
The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean ...
extended across the northern Poland. The area's major conurbation was
Wilno
Vilnius ( , ) is the capital of and List of cities in Lithuania#Cities, largest city in Lithuania and the List of cities in the Baltic states by population, most-populous city in the Baltic states. The city's estimated January 2025 population w ...
, in the northeast of interbellum Poland.
The centre of the country was primarily a huge sparsely-populated swamp, known as
Polesie
Polesia, also called Polissia, Polesie, or Polesye, is a natural (geographic) and historical region in Eastern Europe within the East European Plain, including the Belarus–Ukraine border region and part of eastern Poland. This region shoul ...
. Although it had no roads and few rail lines, it had a supreme strategic importance, as its landscape allowed a prolonged, organized defense. Neither Polesie nor the adjacent
Volhynia
Volhynia or Volynia ( ; see #Names and etymology, below) is a historic region in Central and Eastern Europe, between southeastern Poland, southwestern Belarus, and northwestern Ukraine. The borders of the region are not clearly defined, but in ...
contained any major urban areas.
The south, formerly a portion of the Galicia province of
Austria-Hungary
Austria-Hungary, also referred to as the Austro-Hungarian Empire, the Dual Monarchy or the Habsburg Monarchy, was a multi-national constitutional monarchy in Central Europe#Before World War I, Central Europe between 1867 and 1918. A military ...
, was the most highly-developed area, with ita high density of rail lines, growing amount of industry (such as oil fields in Boryslaw) and well-developed agriculture of
Podolia
Podolia or Podillia is a historic region in Eastern Europe located in the west-central and southwestern parts of Ukraine and northeastern Moldova (i.e. northern Transnistria).
Podolia is bordered by the Dniester River and Boh River. It features ...
.
Lwów
Lviv ( or ; ; ; see #Names and symbols, below for other names) is the largest city in western Ukraine, as well as the List of cities in Ukraine, fifth-largest city in Ukraine, with a population of It serves as the administrative centre of ...
, one of the major cities of interbellum Poland, was located in the area. In addition, the Soviet border was marked by a natural obstacle, the
Zbruch
The Zbruch (; ) is a river in Western Ukraine, a left tributary of the Dniester.Збруч
Upper Silesia
Upper Silesia ( ; ; ; ; Silesian German: ; ) is the southeastern part of the historical and geographical region of Silesia, located today mostly in Poland, with small parts in the Czech Republic. The area is predominantly known for its heav ...
,
Warsaw
Warsaw, officially the Capital City of Warsaw, is the capital and List of cities and towns in Poland, largest city of Poland. The metropolis stands on the Vistula, River Vistula in east-central Poland. Its population is officially estimated at ...
,
Kraków
, officially the Royal Capital City of Kraków, is the List of cities and towns in Poland, second-largest and one of the oldest cities in Poland. Situated on the Vistula River in Lesser Poland Voivodeship, the city has a population of 804,237 ...
or
Poznań
Poznań ( ) is a city on the Warta, River Warta in west Poland, within the Greater Poland region. The city is an important cultural and business center and one of Poland's most populous regions with many regional customs such as Saint John's ...
.
When they developed the plan, Polish planners assumed that co-operation and support would be forthcoming from
Romania
Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...
The Soviet government undermined the validity of the Riga Peace Treaty, which it had signed in 1921, from the outset. In the early 1920s, the Soviets repeatedly organized
guerrilla
Guerrilla warfare is a form of unconventional warfare in which small groups of irregular military, such as rebels, Partisan (military), partisans, paramilitary personnel or armed civilians, which may include Children in the military, recruite ...
attacks on Polish settlements close to the border. The most famous one was the attack on Stolpce, which took place on the night of August 3–4, 1924, which prompted the creation of the ''Korpus Ochrony Pogranicza'' (
Border Protection Corps
The Border Protection Corps () was a military formation of the Second Polish Republic that was created in 1924 to defend the country's eastern borders against armed Soviet incursions and local bandits. Other borders were under the jurisdiction of ...
). Such attacks continued throughout the 1920s but reduced in scale during the 1930s, particularly after the signing of the 1932
Soviet–Polish Non-Aggression Pact
The Soviet–Polish Non-Aggression Pact (, , transliterated as ) was a non-aggression pact signed in 1932 by representatives of Poland and the Soviet Union. The pact was unilaterally broken on September 17, 1939, during the Soviet invasion of P ...
.
Summary
No complete copy of the plan has been preserved. All that is known are the basic precepts, and restoring the whole plan is impossible. Work on the document was completed on February 4, 1939. The plan was based on the notions of
Józef Piłsudski
Józef Klemens Piłsudski (; 5 December 1867 – 12 May 1935) was a Polish statesman who served as the Chief of State (Poland), Chief of State (1918–1922) and first Marshal of Poland (from 1920). In the aftermath of World War I, he beca ...
, who until his death in 1935 was sure that war would come from the east. Thus, most army maneuvers and field fortifications were held in the east, and Poland's western border was largely neglected. Some of the fortifications can still be seen in the area around
Sarny
Sarny (, ) is a small city in Rivne Oblast, western Ukraine. It is the administrative center of Sarny Raion within the oblast and is a major railway node on the Sluch River. Population:
Etymology
The city is named after the roe deer and can ...
(see Sarny Fortified Area). Bunkers built by Polish Corps of Engineers in the 1930s were used in late 1940s by the
Ukrainian Insurgent Army
The Ukrainian Insurgent Army (, abbreviated UPA) was a Ukrainian nationalist partisan formation founded by the Organisation of Ukrainian Nationalists (OUN) on 14 October 1942. The UPA launched guerrilla warfare against Nazi Germany, the S ...
in its guerilla skirmishes against the Soviet
Red Army
The Workers' and Peasants' Red Army, often shortened to the Red Army, was the army and air force of the Russian Soviet Republic and, from 1922, the Soviet Union. The army was established in January 1918 by a decree of the Council of People ...
.
Polish planners were well aware that the Red Army was, in many ways, superior to their own. Therefore, the main idea was to organize a so-called "resistance in motion" and to try to split Soviet forces south and north of the vast Polesie swamps. Frontline armies, in the vicinity of the border, were to try to delay the advance of the aggressors and to bleed them, and reserves, mostly in the areas of
Brześć nad Bugiem
Brest, formerly Brest-Litovsk and Brest-on-the-Bug, is a city in south-western Belarus at the border with Poland opposite the Polish town of Terespol, where the Bug (river), Bug and Mukhavets rivers meet, making it a border town. It serves as ...
and
Lublin
Lublin is List of cities and towns in Poland, the ninth-largest city in Poland and the second-largest city of historical Lesser Poland. It is the capital and the centre of Lublin Voivodeship with a population of 336,339 (December 2021). Lublin i ...
, were intended to enter the conflict in its later stages.
The Poles were expecting the Red Army to advance in three directions: along the
Minsk
Minsk (, ; , ) is the capital and largest city of Belarus, located on the Svislach (Berezina), Svislach and the now subterranean Nyamiha, Niamiha rivers. As the capital, Minsk has a special administrative status in Belarus and is the administra ...
–
Baranowicze
Baranavichy or Baranovichi is a city in the Brest Region of western Belarus. It serves as the administrative center of Baranavichy District, though it is administratively separated from the district. As of 2025, it has a population of 170,817.
...
–
Białystok
Białystok is the largest city in northeastern Poland and the capital of the Podlaskie Voivodeship. It is the List of cities and towns in Poland, tenth-largest city in Poland, second in terms of population density, and thirteenth in area.
Biał ...
–Warsaw rail line, along the Sarny–
Kowel
Kovel (, ; ; ) is a city in Volyn Oblast, northwestern Ukraine. It serves as the administrative center of Kovel Raion within the oblast. Population:
Kovel gives its name to one of the oldest runic inscriptions which were lost during World War II ...
–
Lublin
Lublin is List of cities and towns in Poland, the ninth-largest city in Poland and the second-largest city of historical Lesser Poland. It is the capital and the centre of Lublin Voivodeship with a population of 336,339 (December 2021). Lublin i ...
line and along the
Tarnopol
Ternopil, known until 1944 mostly as Tarnopol, is a city in western Ukraine, located on the banks of the Seret (river), Seret River. Ternopil is one of the major cities of Western Ukraine and the historical regions of Galicia (Central Europe ...
–Lwów line.
Structure of Polish Army
According to the Polish historian Rajmund Szubański, in case of war in the east, the bulk of the Polish Army would be concentrated in the north and the south, with the central section of the border left mostly unguarded. Some military historians claim that Polish planners placed too many units close to the border, which would have resulted in their total destruction in the opening days of the conflict. In contrast, the rear positions were inadequately protected.
Frontline units
Seidner outlines the deployment:Stanley S. Seidner, ''Marshal Edward Śmigły-Rydz Rydz and the Defense of Poland'', New York, 1978, appendices.
* In the extreme northeast, around the rail nexus of
Mołodeczno
Maladzyechna, or Molodechno, is a town in Minsk Region, Belarus. It serves as the administrative centre of Maladzyechna District (and formerly of Molodechno Region from 1944 to 1960). Maladzyechna is located northwest of Minsk. In 2006, it had an ...
Wilno
Vilnius ( , ) is the capital of and List of cities in Lithuania#Cities, largest city in Lithuania and the List of cities in the Baltic states by population, most-populous city in the Baltic states. The city's estimated January 2025 population w ...
Grodno
Grodno, or Hrodna, is a city in western Belarus. It is one of the oldest cities in Belarus. The city is located on the Neman, Neman River, from Minsk, about from the Belarus–Poland border, border with Poland, and from the Belarus–Lithua ...
), two Cavalry Brigades (
Wileńska Cavalry Brigade
Wileńska Cavalry Brigade () was a unit of the Polish Army, created on 1 April 1937 out of the 3rd Independent Cavalry Brigade. Its headquarters were stationed in Wilno (Vilnius), with some regiments garrisoned in the neighboring towns.
In late 193 ...
Suwałki
Suwałki (; ; or סוּוואַלק) is a city in northeastern Poland with a population of 69,206 (2021). It is the capital of Suwałki County and one of the most important centers of commerce in the Podlaskie Voivodeship.
A relatively young ci ...
), and the 5th Air Corps from
Lida
Lida is a city in Grodno Region, western Belarus, located west of Minsk. It serves as the administrative center of Lida District. As of 2025, it has a population of 103,262.
Etymology
The name ''Lida'' arises from its Lithuanian name ''Ly ...
.
* South of Armia Wilno was Armia Baranowicze, with probably four infantry divisions ( 9th Infantry Division from
Siedlce
Siedlce () ( ) is a city in the Masovian Voivodeship in eastern Poland with 77,354 inhabitants ().
The city is situated between two small rivers, the Muchawka and the Helenka, and lies along the European route E30, around east of Warsaw. It is ...
Baranowicze
Baranavichy or Baranovichi is a city in the Brest Region of western Belarus. It serves as the administrative center of Baranavichy District, though it is administratively separated from the district. As of 2025, it has a population of 170,817.
...
Łomża
Łomża () is a city in north-eastern Poland, approximately to the north-east of Warsaw and west of Białystok. It is situated alongside the Narew river as part of the Podlaskie Voivodeship. It is the capital of Łomża County and has been the se ...
Warsaw
Warsaw, officially the Capital City of Warsaw, is the capital and List of cities and towns in Poland, largest city of Poland. The metropolis stands on the Vistula, River Vistula in east-central Poland. Its population is officially estimated at ...
Podlaska Cavalry Brigade
The Podlaska Cavalry Brigade (Polish: ''Podlaska Brygada Kawalerii'') was a military unit of the Polish Army, created on April 1, 1937. Its headquarters were in Białystok, and it was based on the ''Cavalry Brigade Białystok'', existing between F ...
from Białystok) and the 4th Air Corps from
Toruń
Toruń is a city on the Vistula River in north-central Poland and a World Heritage Sites of Poland, UNESCO World Heritage Site. Its population was 196,935 as of December 2021. Previously, it was the capital of the Toruń Voivodeship (1975–199 ...
.
* In the centre was Armia Polesie (also called
Independent Operational Group Polesie Independent Operational Group Polesie (''Samodzielna Grupa Operacyjna Polesie'', SGO Polesie) was one of the Polish Army Corps ( Operational Groups) that defended Poland during the Invasion of Poland in 1939. It was created on 11 September 1939 a ...
Kowel
Kovel (, ; ; ) is a city in Volyn Oblast, northwestern Ukraine. It serves as the administrative center of Kovel Raion within the oblast. Population:
Kovel gives its name to one of the oldest runic inscriptions which were lost during World War II ...
Kobryń
Kobryn or Kobrin is a town in Brest Region, Belarus. It serves as the administrative center of Kobryn District. It is located in the southwestern corner of Belarus, where the Mukhavets river and Dnieper–Bug Canal meet. The town lies about east ...
), one cavalry brigade (
Mazowiecka Cavalry Brigade The Masovian Cavalry Brigade () was a cavalry unit of the Polish Army in the interbellum period, which took part in the Polish September Campaign. It was created on April 1, 1937, out of the former 1st Cavalry Brigade. Its headquarters were in War ...
Poznań
Poznań ( ) is a city on the Warta, River Warta in west Poland, within the Greater Poland region. The city is an important cultural and business center and one of Poland's most populous regions with many regional customs such as Saint John's ...
Kielce
Kielce (; ) is a city in south-central Poland and the capital of the Świętokrzyskie Voivodeship. In 2021, it had 192,468 inhabitants. The city is in the middle of the Świętokrzyskie Mountains (Holy Cross Mountains), on the banks of the Silnic ...
Zamość
Zamość (; ; ) is a historical city in southeastern Poland. It is situated in the southern part of Lublin Voivodeship, about from Lublin, from Warsaw. In 2021, the population of Zamość was 62,021.
Zamość was founded in 1580 by Jan Zamoyski ...
Wołyńska Cavalry Brigade
The Volhynian Cavalry Brigade () was a Polish cavalry brigade, which saw action against the invading Nazi Germany, Germans during the Invasion of Poland (1939), Invasion of Poland, a part of World War II. Raised from recruits in the area of Wołyń ...
from Równe) and the 2nd Air Corps from
Kraków
, officially the Royal Capital City of Kraków, is the List of cities and towns in Poland, second-largest and one of the oldest cities in Poland. Situated on the Vistula River in Lesser Poland Voivodeship, the city has a population of 804,237 ...
.
* In the extreme south was Armia Podole, with five infantry divisions ( 5th Infantry Division from
Lwów
Lviv ( or ; ; ; see #Names and symbols, below for other names) is the largest city in western Ukraine, as well as the List of cities in Ukraine, fifth-largest city in Ukraine, with a population of It serves as the administrative centre of ...
Tarnopol
Ternopil, known until 1944 mostly as Tarnopol, is a city in western Ukraine, located on the banks of the Seret (river), Seret River. Ternopil is one of the major cities of Western Ukraine and the historical regions of Galicia (Central Europe ...
Przemyśl
Przemyśl () is a city in southeastern Poland with 56,466 inhabitants, as of December 2023. Data for territorial unit 1862000. In 1999, it became part of the Podkarpackie Voivodeship, Subcarpathian Voivodeship. It was previously the capital of Prz ...
Jarosław
Jarosław (; , ; ; ) is a town in southeastern Poland, situated on the San (river), San River. The town had 35,475 inhabitants in 2023. It is the capital of Jarosław County in the Subcarpathian Voivodeship.
History
Jarosław is located in the ...
), two cavalry brigades (
Podolska Cavalry Brigade
Podolska Cavalry Brigade (Polish: ''Podolska Brygada Kawalerii'') was a cavalry unit of the Polish Army in the interbellum period. It was created on April 1, 1937 out of the 6th Independent Cavalry Brigade. It took its name from Podolia (Polish: ' ...
from Stanisławów,
Kresowa Cavalry Brigade
Kresowa Cavalry Brigade (Polish: ') was a unit of the Polish Army in the interbellum period. It was organized on April 1, 1937 and was based on the Second Cavalry Brigade. Stationed in the town of Brody, it consisted of several regiments:
* 20th U ...
from
Brody
Brody (, ; ; ; ) is a city in Zolochiv Raion, Lviv Oblast, Zolochiv Raion, Lviv Oblast, western Ukraine. It is located in the valley of the upper Styr, Styr River, approximately northeast of the oblast capital, Lviv. Brody hosts the administrati ...
) and the 6th Air Corps from
Lwów
Lviv ( or ; ; ; see #Names and symbols, below for other names) is the largest city in western Ukraine, as well as the List of cities in Ukraine, fifth-largest city in Ukraine, with a population of It serves as the administrative centre of ...
.
Apart from those units were all of the armies' Border Area Defence Corps units and garrisons of the main cities.
Reserve forces
* Behind Armia Wilno and Armia Baranowicze was Armia
Lida
Lida is a city in Grodno Region, western Belarus, located west of Minsk. It serves as the administrative center of Lida District. As of 2025, it has a population of 103,262.
Etymology
The name ''Lida'' arises from its Lithuanian name ''Ly ...
, with three infantry divisions.
* Behind Armia Podole and Armia Wołyń was Armia Lwów, with two infantry divisions and a cavalry brigade (5th Krakowska BK from Kraków).
* Far behind the frontlines, around the city of Brzesc, was the main reserve, with probably six IDs, two cavalry brigades (7th Wielkopolska BK from Poznań, 8th Pomorska BK from
Bydgoszcz
Bydgoszcz is a city in northern Poland and the largest city in the historical region of Kuyavia. Straddling the confluence of the Vistula River and its bank (geography), left-bank tributary, the Brda (river), Brda, the strategic location of Byd ...
), an armoured brigade and the 1st Warsaw Air Corps.
Red Army along Polish border
In the mid-1930s, the Soviet government started an immense armament program, which resulted in a rapid increase in the number of units. The number of tanks and airplanes along the Polish border grew significantly, and the Soviets enjoyed superiority in all ways. Polish planners anticipated that the Soviets had three times as many soldiers as their
Polish Army
The Land Forces () are the Army, land forces of the Polish Armed Forces. They currently contain some 110,000 active personnel and form many components of the European Union and NATO deployments around the world. Poland's recorded military histor ...
. The Soviets' superiority in tanks and airplanes was not estimated, but the disproportion was immense. In August 1939, along the Polish border were likely as many as 173 Red Army infantry divisions (see
Soviet order of battle for invasion of Poland in 1939
The Soviet order of battle for the invasion of Poland in 1939 details the major combat units arrayed for the Soviet surprise attack on Poland on September 17, 1939. As a result of joining battle after the Germans had already launched their inva ...
).
Invasion of Poland
On September 1, 1939, Germany attacked Poland. Consequently, Plan East became void. On September 17, with a free hand because of the
Molotov–Ribbentrop Pact
The Molotov–Ribbentrop Pact, officially the Treaty of Non-Aggression between Germany and the Union of Soviet Socialist Republics, and also known as the Hitler–Stalin Pact and the Nazi–Soviet Pact, was a non-aggression pact between Nazi Ge ...
, the Soviets broke their non-aggression pact by invading Poland. The Red Army met little resistance, as the Polish Army was concentrated in the west in fighting the Germans. Thus, the Soviets quickly managed to occupy Polish
Kresy
Eastern Borderlands (), often simply Borderlands (, ) was a historical region of the eastern part of the Second Polish Republic. The term was coined during the interwar period (1918–1939). Largely agricultural and extensively multi-ethnic with ...
.
See also
*
Prometheism
Prometheism or Prometheanism () was a political project initiated by Józef Piłsudski, a principal statesman of the Second Polish Republic from 1918 to 1935. Its aim was to weaken the Russian Empire and then the Soviet Union, by supporting natio ...