The Forgotten Attack: Why the Soviet Union Invaded Poland in 1939

In the autumn of that year, a sovereign European state disappeared from the political map of the continent.  Within a few weeks, the second Polish Republic, a country with more than 35 million inhabitants, was divided between two totalitarian superpowers, occupied, and finally destroyed.  The invasion by Nazi Germany on September 1st is considered in most history books to be the beginning of the Second World War.

  But the complete destruction of Poland was not the work of a single power.  Just over two weeks after the German attack in the early morning of September 17, the troops of the Red Army crossed the eastern border of the already heavily beleaguered country.  This blow from the East, which was long overlooked or deliberately concealed in many Western and Eastern narratives,  sealed the fate of the Polish nation.

This report is dedicated to a sober, fact-based examination of those events.  We examine the diplomacy of two totalitarian regimes that cynically set aside their deep ideological differences  to jointly divide a neighbor .  We are following the course of a military operation that began without a formal declaration of war and, in a few weeks, forced an entire country under two occupying powers.

  And we consider the consequences of this division, the annexations, the repressions, and the long-term disruptions that affected millions of people. At that time, the Soviet Union was a totalitarian state under the leadership of Joseph Stalin, having just entered into an alliance of convenience with Nazi Germany, which had been sealed by a treaty in August .

  The aim of this analysis is to demonstrate how this often- forgotten attack completed the liquidation of the second Polish Republic and became part of a joint reorganization of Eastern Europe by two aggressive regimes, with consequences that extended far beyond that year and shaped the lives of entire peoples for decades.  To understand the events of that autumn, one has to look far back to the time immediately after the First World War.

  From the collapse of the old empires, a new Poland had emerged, which had regained its independence after more than 100 years of partition .  But the borders of this young state remained contested for a long time.  In the Polish-Soviet War of 19 to 1900, the young Soviet Republic and the second Polish Republic fought for control of the vast territories between Warsaw and Kyiv.

  The Treaty of Riga in March of that year finally established a border that   awarded large parts of present-day western Ukraine and western Belarus to the Polish state.  In Moscow, however, this treaty was never perceived as fair.  The Bolshevik leadership viewed the eastern vovotariates of Poland as lost territories, as an open wound that would one day have to be closed.

This territorial resentment formed the silent backdrop for everything that was to happen in the following decades .  In the late 1930s, the European order that had been established after the First World War began to falter irrevocably.  The attempt to establish collective security against the growing aggression of Nazi Germany failed due to mutual distrust.

   The Munich Agreement of September 1938, in which Great Britain and France agreed to the dismemberment of Czechoslovakia , left Stalin with a deep aversion.  He concluded that the Western powers were prepared  to sacrifice Eastern Europe to German expansionism and that they might be hoping to steer Hitler eastward against the Soviet Union.

  At the same time, the Red Army had been severely weakened by the great purges of 1937 and 1938 .  Stalin had a significant portion of the senior officers in the Chor arrested and shot , including experienced marshals. The military leadership was unsettled, its fighting strength weakened, and Stalin knew that his armed forces were not yet ready for a major war .

  Against this background, in the summer of 1939 two regimes that were ideologically deeply opposed to each other began to move closer together. Negotiations between the Soviet Union, Great Britain, and France regarding a joint alliance against Germany were hesitant and fruitless.  The Western powers were undecided, and Poland itself strictly refused to   grant Soviet troops the right to march through its territory, out of justified fear that the Red Army would never leave a country once it had entered .  While these talks came to nothing,

 another, more tempting opportunity opened up for Stalin. Nazi Germany, which  was already firmly resolved to attack Poland, urgently needed security in the east to avoid a two-front war.  Thus, two dictatorships, irreconcilably opposed in propaganda and ideology , found each other purely out of a power calculation.

  For both sides, the alliance was a cold, pragmatic deal.  On August 23, the foreign ministers Vateslav Molotov and Joachim von Ribbentrop signed a non-aggression pact between the German Reich and the Soviet Union in Moscow. Externally, this treaty was presented as an instrument of peace, as a guarantee against war between the two powers.

  But the real core of the agreement was hidden in a secret additional protocol, which was concealed from the public for decades and whose existence the Soviet Union denied long after the war.  In this secret protocol, the two regimes divided all of Eastern Europe into spheres of influence.  They determined how the border between the two spheres of influence should run in the event of a territorial reorganization, roughly along the rivers Nare, Vistula and San.

 Finland, Estonia, Latvia and most of Poland east of this line were assigned to the Soviet sphere of influence , while Lithuania and the western part of Poland fell to the German sphere.  Two sovereign neighboring states were secretly divided up here like spoils of war at a negotiating table.  One must fully grasp the significance of this document.

  A treaty that officially bore the name of a non-aggression pact effectively gave the green light for a war of aggression in its secret part.  Without the assurance of Soviet neutrality and without the prospect of the promised spoils from the east, Hitler would hardly have risked the campaign against Poland in this form .

  So how could a pact that proclaimed peace actually open the door to the greatest war in human history?  The answer lies in the nature of the two regimes.  For Nazi Germany, the agreement meant securing its back for the attack against Poland and, in the medium term, against the West.  For Stalin’s Soviet Union, it meant the recovery of those territories that had been considered lost since the Treaty of Rie, as well as gaining time to prepare the weakened Red Army for later conflicts.

  Both sides pursued expansionist goals and both viewed the existence of independent states between them as a mere obstacle.  Just one week later, on September 1st, the German Wehrmacht invaded Poland without a declaration of war.  From the air, from the coast and from the borders in the west, north and south, a modern war of annihilation poured over the country.

  Great Britain and France, which had given guarantees to Poland, declared war on the German Reich two days later , but did not undertake any serious military relief in the west.  The Polish armed forces, brave but technically and numerically inferior, were pushed back in the first weeks, and while the Polish army tried in desperate rearguard actions to build a last defensive zone in the southeast of the country, near the Romanian border,  Stalin waited.

He deliberately delayed his own intervention for several coldly calculated reasons.  Firstly, he did not want the Red Army to appear as an aggressive co-attacker on Germany’s side as long as the Polish government was still capable of acting.  On the other hand, another conflict in the Far East captured his attention.

  Soviet and Japanese troops had been engaged in heavy fighting for months on the Mongolian-Manchurian border at the Shalkhingol River  .  It wasn’t until mid- September that a ceasefire was reached there, which temporarily eliminated the Japanese threat in the east .  No sooner was Stalin’s back free in the Far East than he could take action in the West.  He waited until Poland’s defeat against Germany seemed virtually sealed and the Polish government prepared to flee.

  On the night of September 17th, the Polish ambassador in Moscow was summoned.  He was handed a note in which the Soviet Union claimed that the Polish state and its government had effectively ceased to exist, and therefore all existing treaties with Poland had become invalid . The justification given was that the Red Army felt compelled to cross the border to protect the Ukrainian and Belarusian populations.

The ambassador refused to accept the note, but that did not change the course of events.  This justification was a pretext that stood in sharp contradiction to reality.  The Polish state still existed.  His army continued to fight, and his government, although on the way into exile, had not surrendered.

  Above all, the Soviet attack violated an explicit treaty between Poland and the Soviet Union.  A non-aggression pact had existed since 1932, which was later even extended and was formally supposed to remain valid far into the future. By declaring that the Polish state had ceased to exist, the Soviet leadership attempted to retrospectively conceal the obvious breach of this treaty.

  It was a legal construct designed to make a war of aggression appear as a humanitarian protective measure.   So what drove Stalin to act at that particular moment?  It was a cold calculation that Poland was doomed and that any further delay would only have risked   losing the spoils promised in the secret protocol to the German allies.

  The diplomatic situation thus led directly to military action.  For the invasion, the Soviet leadership had provided two large army groups, which were  called the Belorussian Front and the Ukrainian Front.  The command structures and movements of these units warrant closer examination, as they demonstrate the superiority with which the Red Army invaded an already defeated country.

  In the early morning of September 17, 1939, Soviet troops began  moving along the entire eastern border of Poland.  It was an attack of enormous force against an opponent who barely had any forces left for defense. The numbers speak for themselves .  According to common estimates, the Soviet forces that invaded Poland initially numbered  approximately 400,000 to 500,000 soldiers.

  A fighting force that continued to grow in the following days and is estimated in its entirety to number between 600,000 and over 800,000 men .  They had several thousand tanks and armored vehicles as well as thousands of aircraft at their disposal.  A force that was superior in every respect to the already exhausted Polish defenses in the east , because in the east of the country the Soviet armies faced almost no regular field armies.

  The main forces of the Polish army fought and died in the west against the Wehrmacht. What remained in the east were primarily units of the border guard choir, scattered remnants of defeated units, reservists, police units, and poorly equipped formations without unified leadership.  This overwhelming superiority was no accident, but the result of cool planning.

  The Soviet leadership knew full well that they were not facing an equal opponent, but rather a vacuum that the German attack had already created.  She was able to calmly concentrate her forces at the border , while Polish attention was entirely focused westward.  The Belarusian front was under the command of Mikhail Kovaliovev, while the Ukrainian front was led by Semion Timoshenko, a man who would later play a significant role in the great war against Germany .

  The Soviet leadership’s tactical plan was simple and effective: a rapid, deep breakthrough with mechanized units to  occupy large areas as quickly as possible and to preempt the agreed demarcation lines. Columns of tanks and motorized units rolled far into the interior of the country, often faster than news of the invasion could even spread .

  The Polish defenses here were not prepared for a war in the east .  The original plan to  retreat to the southeast of the country and maintain a resistance zone there, supported by the Romanian border, and to wait for supplies from the Western powers,  finally collapsed with the Soviet invasion.  The so-called Romanian bridgehead, Poland’s last strategic hope, was  destroyed in one fell swoop by the attack from the east.

  Imagine the situation of an ordinary Polish soldier in those days.  For over two weeks, his unit fought, marched, and retreated from the superior German Wehrmacht.  He heard rumors that help might be coming from the east , because many Poles initially hoped that the Red Army might be coming to fight against the Germans .

  This hope was quickly shattered by reality.  When it became clear that the Soviet Union had arrived as the second aggressor, the Polish commanders faced an impossible decision.  The commander-in-chief issued a contradictory and tragic directive , which aimed to avoid fighting the Soviets if possible, except in the event of an attack or an attempt to disarm them, and instead to try to withdraw towards Romania and Hungary.

This directive, born out of a desire to avoid senseless bloodshed, led to confusion in practice.   In some places units surrendered without a fight , in others fierce battles ensued. Despite the hopeless overall situation, individual Polish units put up fierce resistance, and these episodes deserve to be remembered .

  Fighting that lasted several days and resulted in heavy losses broke out around the city of Grotno in the northeast  .  There, soldiers, volunteers, police officers, and even teenagers defended themselves against the advancing Soviet tanks, often with inadequate resources and improvised weapons.  The capture of the city resulted in significant losses for the Red Army, and captured defenders were shot during the fighting .

   There was also fighting around the old city of Vilno , as well as in the region around the town of Schatzk in the east, where units of the border guard choir, under brave leadership, engaged in fierce battles with the Soviet units in the last days of September .  These battles showed that Polish resistance had not completely collapsed, but they remained locally confined, uncoordinated and without any prospect of strategic success.

  A particularly symbolic location was the city of Lemberg, called Lviv in Polish, in the southeast of the country.  This city was initially besieged by German troops , but then, according to the agreements of the secret protocol, it fell under Soviet influence. This led to the dire situation that German and Soviet troops were surrounding the same city and had to coordinate to arrange the handover .

  The Polish garrison, trapped between two attackers, finally surrendered to the Soviet forces in the mistaken hope of being treated more leniently by them than by the Germans.  Many of the captured officers would pay for this decision with their lives.  Elsewhere, Polish cavalry units, the famous Uhlans, fought hopeless battles against the technological superiority, and scattered groups continued the fight for days after the organized collapse.

But why did this resistance ultimately remain so ineffective? Because the overwhelming numerical and technical superiority of the Red Army met a defense that had already been shattered by the German attack, was leaderless and without any reserves. At the same time, the operation also revealed weaknesses within the Red Army itself.

Coordination between the advancing columns was often inadequate, logistics were overloaded, and incidents occurred in which  Soviet units even fired on each other in the general confusion. The rapid advance masked the fact that the army, weakened by the purges,  had significant organizational problems.

  Problems that would prove dire in a real war against an equal opponent .  But these shortcomings hardly mattered against an exhausted Poland. Soviet losses remained  relatively low, considering the scale of the operation.  The number of dead and wounded is estimated at several thousand .  On the Polish side, losses in the east were also considerable.

  But the real catastrophe lay not in the fallen, but in the enormous number of prisoners.  Several thousand Polish soldiers and officers were taken prisoner by the Soviets, a human reservoir whose fate would become tragically significant in the following months .  When the advancing German and Soviet troops met in the interior of the country, the cooperation between the two regimes became visible on the open stage.

  In the fortress city of Brest in Britz, Poland, a joint ceremony took place on September 22nd, during which German and Soviet units commemorated the surrender of the city in an orderly march-past .  Images of this event, showing officers from both armies standing harmoniously side by side, became a lasting symbol of the cynical partnership of those weeks.

A few days later, on September 28, the two powers signed another treaty in Moscow, the so-called Border and Friendship Treaty. In this agreement, they redrawn the final dividing line between their occupation zones, essentially along the Buk and San rivers. As part of this deal, Lithuania shifted from the German to the Soviet sphere of influence, while Germany, in return, received a larger share of central Poland.

  The spoils were remeasured and divided a second time, as if the Polish people had never existed.  The campaign ended with the surrender of the last major Polish units at the beginning of October .  A state with a history spanning over a thousand years, which had only just  enjoyed its regained independence for two decades , had been wiped off the map.

But for the people in the occupied eastern territories, the end of the fighting did not mean peace, but rather the beginning of a new ordeal.  For now the political transformation of the annexed territories began, and this took place with a harshness and systematic approach that revealed the entire nature of the Soviet regime .

  The military operation was over quickly.  The real tragedy of the occupation lasted for years. The Soviet Union immediately set about formally incorporating the conquered territories into its own territory. Elections were hastily organized , the results of which were predetermined and which were intended to create the outward appearance of a voluntary association.

  On this apparent basis, the eastern vovotariates of Poland were assigned to the Belarusian and Ukrainian Soviet republics.  Millions of people who had been citizens of Poland the day before were declared Soviet citizens overnight and subjected to the full power of the Soviet apparatus.  A comprehensive Sovietization began, including the nationalization of land, the dismantling of existing social structures, the suppression of the Catholic Church and national institutions, and the alignment of public life with the Soviet model.  At the

heart of this policy was the terror of the secret service, which at that time was known by the acronym NKVD.  He specifically targeted those groups that were considered potential carriers of national resistance.  Officers, civil servants, landowners, clergy, teachers, judges, police officers and the entire educated upper class.

  In several large waves between the winter  and summer of 1941, thousands of people were torn from their homes and deported in cattle cars to the most remote regions of the Soviet Union, to Siberia in the far north and to Central Asia. The exact number of those abducted remains disputed to this day.  Estimates range from several hundred thousand to well over a million people.

  Many of them, including countless women, children and the elderly, died of hunger, cold, exhaustion and disease.  These deportations fit seamlessly into Stalin’s general nationalities policy , which aimed to uproot and disperse entire populations and to stifle any germ of national self-assertion.  The annexed territories should become a reliably controlled buffer zone .

  The most gruesome chapter of these repressions occurred in the spring of that year. By order of the highest Soviet leadership, several tens of thousands of Polish prisoners of war, mostly officers, but also police officers, border guards, doctors, engineers and members of the educated elite, were systematically murdered in several camps and prisons .

The most famous of these murder sites is located in a forest near the town of Kathy, which is why this crime is still remembered by this name today.   In total, around 22,000 people were killed in this way with shots to the back of the neck and buried in mass graves. It was a deliberate attempt to permanently deprive Poland of its ruling class and thus make any future resurrection of an independent state more difficult.

  For decades, the Soviet Union denied this act and blamed Nazi Germany for it .  until late in the 20th century when Soviet culpability was officially acknowledged.  How did the rest of the world react to this second attack against Poland?  Remarkably reserved.  Although Great Britain and France were already at war with the German Reich because of the German invasion, they did not declare war on the Soviet Union.

 Although the Western powers condemned the Soviet invasion, they did not draw any serious consequences. They wanted to avoid drawing a second powerful adversary into the conflict under any circumstances and secretly hoped that the alliance of convenience between Moscow and Berlin would not last.  Thus, the Soviet attack remained largely without consequences under international law.

  A circumstance that  subsequently confirmed Stalin’s cynical calculation. For the Polish government, which had by then gone into exile, first to France and later to London, this reluctance on the part of the allies was a bitter experience.  They had hoped for support and received words instead of deeds.  The geopolitical caution of the Western powers, who wanted to avoid a confrontation with Moscow at all costs , left Poland alone with its double loss.

  This leniency on the part of the West should be seen as part of the further chain of events, because the aggression did not end with Poland.  The division of Eastern Europe according to the secret protocol continued in the following months. As early as the winter of 1939, the Soviet Union plunged tiny Finland into a war that proved to be far bloodier and more difficult than Stalin had expected, and which exposed the organizational weaknesses of the Red Army to the world.

  In the summer of that year, the Soviet Union finally occupied and annexed the three Baltic states of Estonia, Latvia and Lithuania, as well as parts of Romania. The annexation of Poland in September 1939 was therefore not an isolated incident, but the first step in a whole series of annexations, all   based on the same cynical agreement with Nazi Germany.

  The campaign also provided a military lesson for the Red Army. The identified shortcomings in leadership, coordination, and equipment led to reform efforts, which were far from complete when the alliance between the two dictatorships broke down. Because the alliance of convenience on which all these conquests were based did not hold.

  On June 22, 1941, Nazi Germany invaded the Soviet Union without warning, thereby nullifying the pact and all its secret agreements in one fell swoop.  The territories that Stalin had occupied in the autumn of 1939 were overrun by the German Wehrmacht within a few weeks .  The time that Stalin had hoped to gain through the alliance did not protect the Soviet Union from the German attack.

  On the contrary, the imposed borders and the still incomplete reforms contributed to the fact that the first months of the German-Soviet war were catastrophic for the Soviet Union.  For decades, the memory of the Soviet invasion of Poland was overshadowed by myths and justifications. The official Soviet account did not speak of an attack, but of a liberation campaign to protect the Ukrainian and Belarusian brother peoples from the alleged collapse of the Polish state.

  In this narrative, the Red Army did not appear as a co-attacker alongside Hitler, but as a protector of oppressed nationalities. However, the facts tell a different story.  The Polish state had not yet collapsed at the time of the invasion .  A valid non-aggression pact was broken, and the borders of the occupation zones corresponded exactly to those lines that had previously been secretly agreed upon with Nazi Germany .

  It was the secret agreement between two dictatorships that determined the course of events, not concern for the well-being of any brother nation. What faded from many later accounts of this attack was due to  political reasons.  In the post-war period, when the Soviet Union   was among the victorious powers over Nazi Germany, the memory of its own role as a co-attacker of that year did not fit into the official historical narrative and was therefore suppressed.

  When all these events are considered in context, the outlines of a joint aggression by two totalitarian regimes become clear. The Soviet invasion of Poland was not an isolated incident or a humanitarian protection measure, but the second blade that finally severed a state that was already on its knees .  The cynical interplay between Nazi Germany and Stalin’s Soviet Union resulted in Poland disappearing from the map, accompanied by mass death, deportation, and murder.

  The agreements underlying these events breathed a cold, calculating cynicism, in which the fate of millions of people was reduced to mere bargaining chips between two dictatorships.  The military reality was clear. An overwhelming superiority in manpower and equipment met an exhausted enemy that had been attacked twice .

  And yet, the operation also revealed the deep weaknesses of an army that had previously deprived itself of its best minds.  What remains is the realization that Stalin’s actions that autumn followed a sober calculation of power, the desire for territorial gain, and the preparation for a major war, which nevertheless came and hit the Soviet Union with full force.

  The pact did not protect them from conflict with Germany. He only postponed it by less than two years.  Such forgotten or suppressed attacks reveal the mechanisms by which totalitarian systems expanded in the 20th century , through secret agreements, pretextual justifications, and the ruthless disregard for the sovereignty and lives of entire peoples.

  The partition of Poland serves as a reminder of the price geopolitical deals demand when they are made at the expense of  people’s freedom and livelihoods.  This is a warning that remains valid far beyond that distant autumn and teaches us to look behind the beautiful words of diplomatic treaties and to ask about the intentions that lie hidden in their shadow.  M.