On September 17, 1939, the Red Army crossed Poland's borders, implementing the secret provisions of the Molotov-Ribbentrop Pact. This event, along with the subsequent Soviet troops' entry in 1944, fundamentally changed Poland's fate, leading to the installation of communist rule and significant territorial changes after World War II.

The Red Army's Entry into Poland is one of the most significant events in 20th-century history. This moment not only changed the course of World War II but also shaped Europe's geopolitical map for decades to come.

September 17, 1939, is a date that will forever remain in Polish memory. On this day, in accordance with the secret protocol of the Ribbentrop-Molotov Pact, the Soviet Union began its invasion of Poland's eastern territories. The Red Army crossed the border under the pretext of "protecting" Belarusian and Ukrainian populations, which in reality was the realization of Stalin's imperialist ambitions.

World War II began on September 1, 1939, with Germany's attack on Poland. This conflict quickly evolved into a global one, involving the world's major powers and changing the geopolitical balance of power in the world.

The Ribbentrop-Molotov Pact, signed on August 23, 1939, was a crucial element of pre-war diplomacy. Officially a non-aggression treaty between Nazi Germany and the USSR, it contained a secret protocol dividing Eastern Europe into spheres of influence. Poland found itself at the center of this agreement, with the division line running along the Narew, Vistula, and San rivers. This pact enabled Hitler to start the war without fear of a two-front conflict, while giving Stalin time to strengthen the Red Army.

On September 1, 1939, at 4:45 AM, German forces attacked Poland, beginning World War II. Blitzkrieg, or lightning war tactics, allowed the Wehrmacht to quickly break through Polish defenses. The Luftwaffe conducted devastating air raids on Polish cities, including Warsaw. Despite heroic defense, the Polish army was unable to stop the German war machine. On September 17, Poland's situation dramatically worsened when the Red Army entered from the east, implementing the provisions of the Ribbentrop-Molotov Pact.

Operation Bagration, the largest Soviet offensive in 1944, began on June 23 and led to the breakthrough of the German Eastern Front. This operation was crucial for the liberation of Belarus and the Red Army's entry into Polish territory.

Operation Bagration effectively broke through the German Central Front, utilizing deep battle tactics. Soviet forces, numbering over 2.5 million soldiers, 5,200 tanks, and 5,300 aircraft, quickly overcame German defenses. Key stages of the breakthrough included:

1. Massive attacks on German positions in the Vitebsk, Orsha, and Mogilev regions
2. Exploiting the element of surprise by attacking weaker sections of the front
3. Rapid encirclement maneuvers, cutting off German units' retreat routes
4. Implementation of the "cauldron" tactics, leading to the destruction of large enemy formations

After breaking through the front, the Red Army rapidly advanced westward, achieving significant successes:

Date	Event
July 3, 1944	Liberation of Minsk
July 13, 1944	Capture of Vilnius
July 27, 1944	Entry into Lvov
July 31, 1944	Reaching the Vistula River

The Red Army's advances were characterized by:

1. Rapid pace of advance, reaching 25-30 km per day
2. Effective use of numerical and equipment superiority
3. Cooperation between different military branches, including air force and artillery
4. Flexible command structure enabling quick responses to changing front situations

Operation Bagration led to the complete collapse of the German Army Group Center and opened the way for the Red Army into Poland and further west, changing the balance of power on the Eastern Front of World War II.

The Red Army entered Polish territory at two crucial moments during World War II. The first entry occurred on September 17, 1939, and the second as part of Operation Bagration in 1944.

The Red Army crossed the Polish border along its entire length from Polotsk in the north to Kamianets-Podilskyi in the south. Soviet forces, numbering approximately 600,000 soldiers, 4,700 tanks, and 3,300 aircraft, attacked along a 1,400-kilometer front. The invasion began at 3:00 AM, catching Polish defensive forces by surprise, as they were already engaged in combat with the German aggressor in the west.

September 17, 1939, marks the official date of the Red Army's entry into Polish territories during the first invasion. The Soviet aggression occurred 16 days after Germany's attack on Poland. In 1944, during Operation Bagration, the Red Army entered Polish territories again. On July 22, 1944, Soviet troops crossed the Bug River, entering pre-war Polish territory. On August 1, 1944, Soviet units reached the outskirts of Warsaw, stopping on the eastern bank of the Vistula River.

The Red Army's entry into Poland triggered complex reactions and far-reaching consequences. These events influenced the attitudes of the Polish resistance movement and led to the establishment of new political structures under Soviet supervision.

The Polish resistance movement reacted to the Red Army's entry with mixed feelings. Initially, some groups viewed the Soviets as potential allies in the fight against Nazi Germany. However, it quickly became clear that the Red Army was pursuing its own political objectives. The Home Army, the largest underground organization, adopted a strategy of limited cooperation known as Operation "Tempest". It involved revealing themselves to the Soviets as the legitimate hosts of the territory while maintaining caution about their intentions. This tactic proved ineffective, as the NKVD began arrests and deportations of Polish underground members. The resistance movement's attitude toward the Soviets changed dramatically, shifting from conditional cooperation to open hostility and resistance.

On July 21, 1944, with the advancement of the Red Army, the Polish Committee of National Liberation (PKWN) was established. The PKWN, created on Stalin's initiative, was meant to counterbalance the Polish government-in-exile in London. The Committee consisted of Polish communists and left-wing activists loyal to the Soviet Union. PKWN issued a manifesto declaring itself the temporary executive authority in the liberated territories of Poland. This document contained promises of social and economic reforms aimed at gaining public support. The establishment of PKWN was a crucial step toward installing a communist government in post-war Poland, which met resistance from a significant portion of society loyal to the legitimate government-in-exile.

The Red Army's entry into Poland in 1944 had a fundamental impact on shaping the country's post-war reality. The Soviet military presence enabled the introduction of profound political, social, and territorial changes.

The Red Army played a crucial role in establishing the communist regime in Poland. The Polish Committee of National Liberation (PKWN), formed on July 21, 1944, became an instrument of the country's Sovietization. The PKWN, supported by Soviet armed forces, began the process of eliminating political opposition and introducing systemic changes. The communists systematically took control of key state institutions, administration, and economy. Agricultural reforms and industrial nationalization were carried out under Soviet supervision. The security apparatus, modeled on the NKWD, effectively suppressed all manifestations of social resistance.

The presence of the Red Army enabled radical shifts in Poland's borders. Under the provisions of the Yalta and Potsdam conferences, Poland lost its Eastern Borderlands to the USSR. In exchange, it was granted territories in the west and north, known as the Recovered Territories. The new eastern border was drawn along the so-called Curzon Line. Poland gained access to the Baltic Sea, including Western Pomerania, Warmia, and Masuria. The western border was established along the Oder and Lusatian Neisse rivers. These territorial changes were associated with mass population transfers, leading to profound demographic and cultural transformations.

The Red Army's entry into Poland in 1939 and 1944 marked a crucial moment in the country's history. These events not only influenced the course of World War II but also shaped Poland's post-war reality.

The Soviet military presence enabled profound political, social, and territorial changes. It led to the establishment of a communist regime, elimination of opposition, and radical shifts in the country's borders.

These events left a lasting mark on Polish national consciousness and continue to influence contemporary Polish-Russian relations. Understanding these historical processes is crucial for a complete picture of Polish 20th-century history.