Complex sentence: During Barbarossa, the operational guidelines for mass anti-Jewish actions were issued by Reinhard Heydrich, who ordered his "Einsatzkommando" chiefs to implement them on territories newly occupied by the German forces.
Split into simpler sentences: During Barbarossa, the operational guidelines for mass anti-Jewish actions were issued by Reinhard Heydrich. His "Einsatzkommando" chiefs were ordered to implement them on territories newly occupied by the German forces.