Germany invaded Poland on 1 September 1939, marking the beginning of World War II.

On 17 September 1939 the Soviet Union, then an ally of Germany, invaded Poland from the east.

[3] They encountered only limited resistance, as the majority of Polish forces were thinly stretched against the German invaders.

[1] The group encountered the Soviets on September 28 near the village of Jabłoń, while advancing south towards Parczew.

As the Polish units advanced towards Milanów, they defeated another Soviet attack, inflicting significant casualties on the enemy and taking a number of prisoners.