The potential use of military force in Syria and its past use in Kosovo -- despite the likely "illegality" under international law and the U.N. Charter -- raise important general questions about the modern, post-WWII attempt to establish "rule of law" constraints on the inter-state use of force. Jack and Ashley have noted the widespread view, then and now, that the Kosovo bombings were "technically" illegal under international law, but nonetheless right. Absent Security Council approval, the same might be true regarding Syria.
Thus, what should the role of the international "rule of law" be in constraining the exercise of military power in exceptional contexts, such as those involving the use of force or response to serious security threats?
In my view, part of the reason the relationship between law/morality/political judgment is so much more difficult in these international use-of-force contexts has to do with fundamental differences we often forget (or take for granted) regarding the rule of law in the ordinary domestic legal system. In domestic legal systems, law deals with regularly recurring contexts, such as contract disputes; through judicial decision-making and practices developed over time, the law can work itself out over similar, repeating cases. The evolution of legal principle can occur through a trial and error process, in which pragmatic learning from experience, too, plays an important role.
But when dealing with issues like whether to use military force in Kosovo, or Libya, or Syria, each specific set of circumstances is simply too singular, too contextual, and the situations do not recur repeatedly in the same or closely related form. Moreover, the stakes - security stakes, political stakes, international relations stakes - could not be higher. The issue then becomes about the appropriate role of law -- the "rule of law" -- in highly unique settings where the costs of politico-legal systems getting the answer "wrong" are momentous and not easily reversible.
In the modern era, since WWII, we have wanted to reduce these international tensions into formal, written legal "rules" that can be codified in texts like the U.N. Charter. Shortly after 9/11, I wrote a piece, called The Dark Side of Legalism, 44 Va. J. Int'l L. 145 (2003)(apparently I never posted this on SSRN), trying to point out there are also costs that can result from thinking that formal, written legal rules that try to regulate in advance what is permitted in these unique, non-recurring, high-stakes contexts. Given how much the Kosovo example informed my analysis, and how much it informs today's debates regarding Syria, here are a few excerpts:
In some contexts, unwritten norms can be more effective constraints, precisely because they enable a desirable flexibility for dealing with exceptional contexts involving political power. . . .
Indeed, advocates of formal legal codification as a solution to problems of political power sometimes trade too easily on an implicit or explicit claim that the only alternative to law is force and chaos. Instead, the alternative to a legal text such as the UN Charter is a world in which limitations on state use of force are left to debate, determination, and enforcement through the system of international relations itself. . . . The choice is between the greater rigidity (and loss of flexibility) that tends to come with formal codification and the greater flexibility (and opportunity for unprincipled exercise of power) that comes from a less text-bound system of general principles of international relations. ...
We should ask, for example, whether the multilateral military intervention in Kosovo that eventually took place (or the international intervention that never did take place in Bosnia) would have been easier to bring about - and many more lives have been saved - had the general norm against state use of force or the mechanisms by which collective force was mobilized been left to political debate and practice, rather than being codified into the form of a strong legal rule embodied in the UN Charter. Would a more flexible interpretation of this principle have been easier to achieve if the general "rule" had been left expressed as a norm instead of being turned into a textually embodied, formal rule of international law? . . .
First, the Security Council had to decide whether the conditions that justified collective deployment of force were present in the Kosovo context. Second, once the Security Council failed to come to that conclusion, the further decision had to be made whether the collective use of force by NATO, not endorsed by the Security Council, nonetheless complied with the Charter. ...
Would collective action to stop the ethnic cleansing in Kosovo have emerged more quickly had the codified provisions of the UN Charter not stood in the way? [Update: I believe roughly a year was spent debating the intervention, including its legality] It is impossible to know, given the relationship between material national self-interest and rule-of-law like considerations in the actions and discourse of states in this area. Would the arguments against intervention have been considered less forceful if the rules of the Charter had not been codified in text but instead existed as softer principles of international relations? If codification of these rules against the use of collective force (except with Security Council authorization, and even then, for perhaps only limited purposes), contributed to inaction or delay in any of these humanitarian contexts in recent years, that would be a serious cost of legal formalization that must be taken into account.
Again, remember that we are dealing with relatively exceptional, singular contexts. . . . There is a critical question of whether legalization of norms has, as a dark side, the reduction in flexible interpretation of the underlying norms in new contexts. We ought not to preclude that debate by an overly simple assumption that more law, or more legalization, is always to the good. Perhaps the advantages of general, written rules, despite how over-or under-inclusive they might be - justifies this loss of flexibility; perhaps the relevant actors are likely to be just as appropriately flexible with law as they are with norms. But we need to consider these questions before simply assuming that legalization, clarity, and textual commitment are unadorned virtues.