In August 1942 during Case Blue, the German offensive in southern Russia, he was appointed commander of Army Group B. In 1944, Weichs commanded Army Group F in the Balkans overseeing the German retreat from Greece and most of Yugoslavia. During the Nuremberg Trials, Weichs was implicated in war crimes committed in the Balkans and was scheduled to take part in the US Army's Hostages Trial. He was removed from the proceeding for "medical reasons" without having been judged or sentenced.