Complex sentence: The Germans referred to a "Schwerpunkt" (focal point and also known as "Schwerpunktprinzip" or concentration principle) in the planning of operations; it was a center of gravity or point of maximum effort, where a decisive action could be achieved.
Split into simpler sentences: The Germans referred to a "Schwerpunkt" (focal point) and to a "Schwerpunktprinzip" (concentration principle) in the planning of operations. They viewed the "Schwerpunkt" as a center of gravity or point of maximum effort, where a decisive action could be achieved.