Although the tree happens to have emerged from using decision modeling methods to think about crises, conflicts, and deterrence, none of the factors in the tree is truly remarkable. The tree could have been assembled by merely combining ideas from a dozen texts and articles in international relations. However, viewing deterrence as influencing human beings operating in politically rich contexts has the effect of increasing the weight one puts on several of the factors, which are often mentioned in lip service and then discarded. Moving from left to right, we see that deterrence is served if the would-be aggressor has no compelling incentives to invade and if there are moral and cultural considerations that argue against invasion. These factors may remind us that Canadians do not lose sleep worrying about invasion by the United States; nor do the Low countries in Europe currently worry about historical enemies repeating their deeds. Moving rightward again in Figure G. 1.1, deterrence is served if there is fear of military defeat in an invasion attempt and if there is fear of other consequences even if "success" is likely. At the next level of detail there are some important distinctions, but what matters most to this discussion is recognizing that we must be serious about all of the factors, not merely list them and then move on to the more straightforward of military issues. Why? Because both history and analysis indicate that depending on extended deterrence by denial (being able to defeat invasion) to protect non-vital interests is probably a losing proposition. In some cases, deterrence by denial is not even militarily feasible. In other cases, it is politically very questionable because it requires prompt and decisive multilateral actions under ambiguous circumstances.