Bock had risen through the ranks of the German Army to become, alongside RUNDSTEDT and LEEB, one of the three Army Group Commanders. In the Polish Campaign, Bock was in command of Army Group North which swept aside the Polish units. In the campaign in the west he commanded Army Group B which overran Belgium and Holland and broke the line of the Lower Seine in the Battle of France. Bock’s next command was of Army Group Center, which advanced from Poland to Moscow in the second half of 1941. Bock hopelessly overextended his lines and his men were completely exhausted, Bock himself was suffering from stomach cramps and could not properly exercise his command. Along with Rundstedt and other senior Generals he was purged following the Soviet counteroffensive outside Moscow in December 1941. However early in 1942 REICHENAU suffered a stroke at his Headquarters and Bock was recalled to take command of Army Group South in the USSR. While in command of the German drive into the Caucasus in July 1942, he was dismissed following a dispute with Hitler.