While in command of the 6th Army during Operation Barbarossa in 1941, he issued the notorious Severity Order which encouraged German soldiers to murder Jewish civilians on the Eastern Front.

Reichenau's troops cooperated with the SS Einsatzgruppen in the commission of the massacre of over 33,000 Jews at Babi Yar, and assisted with other crimes against humanity that occurred in areas under his command during the Holocaust.

Reichenau's early years are described in conflicting terms, as both progressively minded but also brutal, with a history of executing soldiers who were AWOL, even in times of peace.

Greatly unconventional, he was an avid outdoors man, spoke English at home and, in contrast to his later activities in Russia, insisted on supporting World War I Jewish veterans' events in full military uniform, even after Hitler came to power.

After the war, he joined the Grenzschutz Ost Freikorps as a General Staff officer, serving in Silesia and Pomerania.

[3] As an outspoken ally and advocate of Hitler and the Nazi Party, Reichenau soon ran afoul of cabinet member and eventual Chancellor Kurt von Schleicher, who used his authority to have him transferred out of his prestigious posting in Berlin to the headquarters of the military district of East Prussia, a relative backwater.

He played a leading role in persuading Nazi leaders such as Göring and Himmler that the power of Ernst Röhm and the SA must be broken if the army was to support the Nazi-led government.

"[11] In November 1941 Hitler relieved Field Marshal von Rundstedt from his command of Army Group South and promoted Reichenau to take his place.

[13] He then sustained severe head injuries when the flight carrying him back to Leipzig for medical attention crashed on landing in Lemberg.

Having died in 1942, Reichenau was never convicted of war crimes, but he was part of the German General Staff and High Command of the Armed Forces collectively indicted at Nuremberg.

[14] Reichenau was in charge of the area of operations in which SS, Einsatzgruppen, and Ukrainian auxiliaries committed the massacre of over 33,000 Jews at Babi Yar.

Later that year in August, Reichenau also directly acted to ensure the execution of ninety Jewish children in the Bila Tserkva massacre, after Helmuth Groscurth petitioned him to avert the killings.