 Complete the following phrase:  During the German invasion which began on 1 September 1939, Sosnkowski proposed forming a group of armies in the region of Warsaw and Kutno, in order to tie-up the German forces there. His ideas were rejected by Rydz-Śmigły, which may have had resulted in uncoordinated military activity and eventually the Polish defeat in the Battle of the Bzura. Only on 11 September he was appointed commander of the Southern Front. Retreating toward Lwów, he conducted several victorious engagements with German forces. The 