Final answer:
The detail of planning for military commanders is most significantly determined by the quality of intelligence gathering, which informs strategic decisions and the coordination of large military forces.
Step-by-step explanation:
The factor that determines the detail to which the commander and staff can plan more than any other is intelligence gathering. A profound understanding of the enemy's capabilities, locations of troops, and intentions, facilitated through espionage and reconnaissance, informs military strategies and operations to an extensive degree. Military organizations depend on high-quality intelligence to create effective plans and adapt them rapidly to dynamic circumstances on the battlefield. Having accurate intelligence allows for precise coordination of vast numbers of troops and support, which is crucial in modern warfare where complexity and the scale of operations are immense. The examples from history and military theory across different sources, including the reliance on intelligence within the U.S. government and the role of spies as mentioned in ancient military texts, illustrate the undiminished importance of good intelligence in military planning.