Lesser Poland was defended by the following Polish armies : After a few days the Battle of the Border was lost , and forces of German Army Group South advanced deep into Lesser Poland 's territory . Polish troops resisted fiercely , and among major battles in initial stages of the war , which took place in Lesser Poland , there are Battle of Mokra , Battle of Jordanów , and Battle of Węgierska Górka . By 6 September , Polish forces were in general retreat and Marshal of Poland Edward Rydz-Śmigły ordered all troops to fall back to the secondary lines of defences at the Vistula and San Rivers . German units entered Częstochowa on 3 September ( where on the next day they murdered hundreds of civilians ) , Kielce on 5 September , Kraków on 6 September , and Radom on 8 September ( see also Battle of Radom ) . Within a week , almost whole Lesser Poland was under Nazi occupation . Northeastern part of the province , the area of Lublin , was held by the Poles until 17 September , but eventually , and after fierce battles ( see Battle of Tomaszów Lubelski ) , all Lesser Poland was firmly under Nazi control . First draft of Molotov – Ribbentrop Pact stipulated that northeastern Lesser Poland ( east of the Vistula river ) was to be occupied by the Soviet Union , and forces of the Red Army reached the area of Lublin after 20 September , but withdrew east on 28 September
murdered hundreds of civilians
Częstochowa massacre
Lesser Poland