Coercion simply means compelling adversaries to do something, while deterrence is dissuading opponents from doing something. Together, these strategies constitute the fundamental dynamic driving most peacetime and wartime situations, at the highest echelons of diplomacy as well as the lowest levels of tactics. From the standpoint of military strategy, it is rarely sufficient to compel one’s foes to do something; usually one must also deter them from doing something else. Both strategies require similar conditions for success: reliable knowledge of one’s opponent, credible military power, active monitoring, and some shared communications and expectations. Without the latter two especially, both deterrence and coercion are vulnerable to unanticipated events.