Be pretty if you are,
Be witty if you can,
But be cheerful if it kills you.
It may be too simple to reduce the argument to just two sides—those who fear the regime's acquisition of nuclear weapons more than the consequences of a war to prevent it, and those who fear the consequences of a war above all else—but in this case simplicity has the virtue of capturing the essence as observers ponder which set of unpalatable risks they would rather run. What is remarkable, though hardly surprising, is that the two sides usually put forth very different assessments of what using force would entail. Those who fear Iranian nukes above all else tend to minimize the risks of using force, while those who fear war tend to exaggerate them. Neither side, however, has persuasively spelled out the reasons for their assessment, leading one to suspect that much of the argument rests on less than rigorous analysis.
What would an honest assessment of the risks of military conflict with Iran look like? How should we think about it? These are difficult questions even for those who are not partisans of one side or the other. Wars are notorious for yielding unintended and unexpected consequences; for reasons explained below, a war against Iran is even harder than usual to bound analytically.At least three concepts are key to any coherent discussion of a U.S.-Iranian military engagement: complexity, uncertainty and war itself. By complexity we mean the number of moving parts in a given situation: actors, processes and the connections among them. By uncertainty we mean structural uncertainty—that is, not just ignorance of the magnitudes of agreed casual factors, but the ignorance of the causal factors themselves, and their mutual relations. For example, not only may the U.S. government not know, say, the technical status of the Iranian nuclear program, or the actual state of readiness of Iranian forces. It may not know (or worse, have wrong) the decision-making and implementation protocols of the Iranian government, how the Iranian people and military would react to an attack, what Tehran would ask its allies and proxies to do, and what in fact they will do.
As to the meaning of war, it may hardly seem worthwhile to probe something so self-evident, except that it is not self-evident anymore, if it ever was. A simple definition of war is the waging of armed conflict against an enemy, but this is too limited a concept in the 21st century. War in our time involves simultaneous conflict in the military, diplomatic, economic and social domains on four levels: political, strategic, operational and tactical.3 While a war with Iran might begin in the military domain, it would likely expand to others, and while it might begin at the operational or tactical level it would soon encompass strategic and political levels as well.
How these twin expansions would take place has everything to do with context. All wars have one. Would a U.S.-Iran war break out during a protracted diplomatic process, or in the absence or abeyance of one? Would it happen during a period of increasing tension and military readiness, or out of the blue, after one party thinks that the dangers of war have subsided? Would the U.S. government assemble a broad "coalition of the willing", just a few close allies-in-arms at the ready, or go it alone, even actively dissuading Israel from joining an attack? What would the domestic political situation be in the United States? Would there be an internal political consensus to act, or would there be an active, acrimonious debate? Would the American people be prepared for the aftermath of an initial attack, including rising oil prices and falling stock values? What would the economic situation be like in the United States and beyond? The answers to these questions would have a substantial impact on the war's course, conduct and outcome.