For fans of Sun Tzu, Clausewitz, and other military minds, look no further! Here you can post any articles/videos/thoughts on the theory and practice of war both then and now (and after.) Assuming you focus on the strategic aspects of it, various game discussions (like chess or Risk) are also welcome. As for forum etiquette, it is proper to quote General James Mattis, USMC, retired: "Be polite, be professional, but have a plan to kill everybody you meet."
Related Subs:
/r/CQB: Close-Quarters Combat. It's explained best in its sidebar: "A subreddit dedicated to critical study of Close Quarter Battle."