On September 17, 1939, the Soviet Union, breaking existing international treaties, launched a military invasion of Poland. The attack was the implementation of the secret protocol of the Ribbentrop-Molotov Pact and occurred when Poland was fighting a desperate battle against Nazi Germany. About 600,000 Red Army soldiers, supported by 4,700 tanks and 3,300 aircraft, crossed Poland's eastern border, beginning a period of Soviet occupation and mass repression against civilians.

September 17, 1939, is a date forever etched in Polish history as the day of a double invasion. While Poland desperately defended itself against Nazi Germany's attack from the west, the Soviet Union unexpectedly struck from the east.

This coordinated attack was the result of a secret protocol in the Ribbentrop-Molotov Pact, signed just a week before the outbreak of World War II. The Soviet aggression against Poland was not only a violation of existing treaties but also marked the beginning of a tragic chapter in the country's history. This event had far-reaching consequences, shaping the geopolitical situation of Central and Eastern Europe for decades to come.

The Ribbentrop-Molotov Pact, signed on August 23, 1939, was a crucial event preceding the outbreak of World War II. This seemingly innocent non-aggression treaty between Nazi Germany and the Soviet Union concealed a secret protocol that had dramatic consequences for Poland and other Central and Eastern European countries.

The secret protocol of the Ribbentrop-Molotov Pact contained detailed arrangements for the division of Eastern Europe between Germany and the USSR. Poland was divided along the Narew, Vistula, and San rivers. The territories west of this line were to be given to Germany, and the eastern areas to the Soviet Union. This division resulted in:

• The liquidation of the Polish state
• The annexation of 51% of Poland's territory by the USSR
• Soviet control over 13 million Polish citizens

The secret protocol was a clear violation of:

1. Polish sovereignty
2. International non-aggression treaties
3. Principles of international law

Its existence was consistently denied by the USSR until 1989, when they officially admitted to signing it.

The Soviet attack on Poland began on September 17, 1939, at 3:00 in the morning. This date was written in black letters in Polish history, symbolizing the beginning of Soviet occupation and the tragic fate of millions of Poles.

On September 17, 1939, the Red Army crossed Poland's eastern border along its entire length. Approximately 600,000 Soviet soldiers, supported by 4,700 tanks and 3,300 aircraft, entered Polish territory. The invasion began at dawn, catching Polish forces unprepared and concentrated on defending against the German attack. The Polish government, surprised by the aggression from the east, ordered a withdrawal towards the Romanian border, avoiding open combat with the Red Army.

The Soviet aggression against Poland in 1939 was the result of a complex geopolitical situation and the USSR's strategic interests. This attack had deep roots in the Soviet Union's foreign policy and its relations with Nazi Germany.

The USSR's attack on Poland was a direct consequence of the secret protocol of the Ribbentrop-Molotov Pact. This document, signed on August 23, 1939, contained detailed arrangements for the division of Eastern Europe between the Third Reich and the Soviet Union. Poland was divided along the Narew, Vistula, and San rivers, giving the USSR control over the eastern part of the country. The implementation of the pact included:

• Annexation of 51% of Poland's territory by the USSR
• Taking control over 13 million Polish citizens
• Elimination of the Polish state as a sovereign entity
• Military cooperation with Germany to quickly defeat Polish armed forces

The attack on Poland stemmed from the broader strategic interests of the Soviet Union in the region. The USSR aimed to:

1. Expanding the sphere of influence in Central and Eastern Europe
2. Creating a security buffer between its borders and Germany
3. Reclaiming territories lost after World War I
4. Preventing a potential alliance between Poland and Germany against the USSR
5. Gaining access to natural resources and industrial capabilities of eastern Poland

This strategy aligned with the USSR's long-term policy aimed at strengthening the country's position in the international arena. The aggression against Poland was a key element in achieving these goals, enabling the USSR to significantly expand its territory and influence in the region.

The Soviet invasion of Poland began on September 17, 1939, at 3:00 AM. The Red Army crossed the border along its entire length, thus beginning the occupation of the eastern part of the country.

The first clashes on the eastern border were characterized by the rapid advance of Soviet troops. The Border Protection Corps, numbering only 20,000 soldiers, was unable to effectively oppose the overwhelming forces of the Red Army. Soviet armored units quickly broke through the weak defense line, penetrating deep into Polish territory. Cities such as Vilnius, Grodno, and Lviv became immediate targets. Within the first 24 hours of the invasion, Soviet troops advanced 50-60 kilometers into the country, capturing key strategic points.

The Polish Command's response to the Soviet invasion was limited and chaotic. The Commander-in-Chief of the Polish Armed Forces, Marshal Edward Rydz-Śmigły, issued an order to avoid combat with the Red Army, except in cases of attempted disarmament or necessary self-defense. Polish units were instructed to withdraw toward the Romanian and Hungarian borders. This decision was driven by the hope of reorganizing forces in allied Romania and the desire to avoid fighting on two fronts. The Polish government, along with President Ignacy Mościcki, left the country, crossing the Romanian border on the evening of September 17. The lack of unified command and clear orders meant that many Polish units were left to fend for themselves, resulting in local resistance attempts or surrender.

The Soviet attack on Poland on September 17, 1939, had far-reaching consequences for the country and its inhabitants. The aggression from the east dramatically changed Poland's military situation and affected the fate of millions of civilians.

The Soviet attack completely collapsed Polish defense. The Red Army, numbering 600,000 soldiers, 4,700 tanks, and 3,300 aircraft, quickly broke through the weak defense line in the east. Within 24 hours, Soviet troops advanced 50-60 km into the country. Polish forces, already weakened by the fight against Germany, were unable to effectively oppose the second aggressor. Marshal Edward Rydz-Śmigły issued an order to avoid fighting with the Red Army, which led to many units withdrawing without a fight. The result was the rapid occupation of eastern Poland by the USSR, including key cities: Vilnius, Grodno, and Lviv.

The Soviet attack had tragic consequences for the civilian population. The USSR annexed 51% of Poland's territory, taking control of 13 million Polish citizens. Mass deportations, arrests, and executions began. Between 1939-1941, the NKVD deported approximately 320,000 Poles to Siberia and Kazakhstan. Four main waves of deportation were carried out: February 10, April 13, June-July 1940, and May-June 1941. Hundreds of thousands of civilians were subjected to repression, including intellectuals, state officials, officers, and their families. The Katyn massacre, in which about 22,000 Polish officers and elite representatives were murdered, became a symbol of these repressions. The civilian population also experienced forced Sovietization, property confiscation, and religious persecution.

The USSR's attack on Poland on September 17, 1939, provoked varied reactions in the international arena. Most Western states, focused on the conflict with Germany, adopted a passive stance toward Soviet aggression.

Great Britain and France, despite their guarantees to Poland, took no concrete actions against the USSR. The governments of these countries, bound by their declaration of war against Germany, avoided confrontation with Moscow. Official statements were limited to expressing concern, without condemning the aggression or imposing sanctions.

The United States, then neutral in the European conflict, also did not take decisive steps. President Franklin D. Roosevelt publicly expressed regret over Poland's fate, however, the USA did not decide to intervene diplomatically or economically against the USSR.

The Baltic and Scandinavian states, fearing Soviet expansion, maintained restraint in their official responses. Estonia, Latvia, and Lithuania, threatened by a similar fate, avoided criticizing the USSR. Finland, aware of the threat from Moscow, intensified its defensive preparations.

Germany, bound by the Ribbentrop-Molotov Pact, officially accepted the USSR's actions. Italy, Germany's ally, did not express opposition to the Soviet aggression. Japan, surprised by the German-Soviet alliance, maintained neutrality on this issue.

The League of Nations, weakened and unable to act effectively, took no significant steps in response to the USSR's attack. The organization limited itself to expressing formal condemnation of the aggression, without practical consequences for the aggressors.

International reactions to the USSR's attack on Poland were characterized by restraint and lack of concrete actions. Most countries, focused on the conflict with Germany or fearing escalation of tensions, adopted a passive stance, which de facto enabled the USSR to implement its territorial expansion plans.

• On September 17, 1939, the Soviet Union attacked Poland from the east, implementing the secret protocol of the Ribbentrop-Molotov Pact.
• The USSR's attack was coordinated with the German invasion and led to the division of Polish territory between the two aggressors.
• The Red Army quickly broke through Poland's weak eastern defenses, occupying key cities and territories.
• The attack resulted in mass deportations, repressions, and crimes against Polish civilians, including the Katyn massacre.
• International reactions to Soviet aggression were restrained, enabling the USSR to implement its territorial expansion plans.
• This event had far-reaching consequences, shaping the geopolitical situation of Central and Eastern Europe for decades to come.

The Soviet Union's attack on Poland on September 17, 1939, marked a turning point in the history of World War II. This event not only sealed Poland's fate but also changed the balance of power in Central and Eastern Europe.

The secret protocol of the Ribbentrop-Molotov Pact proved to be a key factor that enabled the USSR to achieve its strategic goals. The lack of a decisive response from the international community allowed for the rapid annexation of Poland's eastern territories.

The consequences of this aggression were tragic for millions of Poles who experienced deportation, persecution, and mass executions. These events shaped Polish-Soviet relations for years to come and influenced the geopolitical landscape of the region.