Final Answer:
The central idea of the text indicates that the primary duty of soldiers is to serve and protect their nation, highlighting the need for cautious and humane military management.
Step-by-step explanation:
The central idea of the text is best described by Option B: Above all, soldiers duties are to serve and protect their country. This idea is reflected in various parts of the text, which emphasize the importance of caution and humanity in warfare, the obsolescence of traditional combat due to mechanization, and the necessity for soldiers to be treated humanely yet with strict discipline. The text implies that the focus should be on the protection of the country and the careful management of the military to prevent unnecessary loss and maintain peace, rather than engaging in war for personal or political reasons.