Complex sentence: With Himmler in charge, the practical effect was that "Oberkommando Oberrhein" answered directly to Hitler, introducing a disadvantageous schism in high command for German Western Front operations.
Split into simpler sentences: With Himmler in charge, the practical effect was that "Oberkommando Oberrhein" answered directly to Hitler. This introduced a largely disadvantageous schism into the high command for German Western Front operations.