Complex sentence: While Hitler had been still alive, Dönitz had followed absolutely his commands to fight on to the last on all fronts, but he now saw that surrendering German forces only to the Western Allies could present opportunities to split the British and Americans from the Soviets.
Split into simpler sentences: While Hitler had been still alive, Dönitz had followed absolutely his commands to fight on to the last on all fronts. He believed that surrendering German forces only to the Western Allies could present opportunities to split the British and Americans from the Soviets.