During the invasion of Poland, the 8th Army under Blaskowitz's command was responsible for the northern part of the front under Army Group South, led by Gerd von Rundstedt. The 8th Army saw heavy combat during the Battle of the Bzura and later besieged the Polish capital of Warsaw. After the campaign, he was awarded the Knight's Cross of the Iron Cross, promoted to Generaloberst and appointed as Commander-in-Chief East in Poland on 20 October 1939.