Whatever the objective U.S. policy makers select, forming a credible international coalition will be essential to achieving those objectives. A credible coalition is marked both by substantial numbers of supporters and participants; regional “anchor” nations must actively support, and even participate in, actions; and globally-influential governments must, at a minimum, not object to coalition actions. Certainly Syria’s neighbors must participate. It is essential that some key Islamic governments actively support a coalition, lest U.S. actions be perceived as primarily fighting Islam and securing Israel.
Absent a coalition, U.S. actions taken alone will be perceived as illegitimate and therefore may even be counter-productive to achieving the over-arching political objective. If the international consensus is that the U.S. is inserting itself as a combatant into the Syrian civil war, Assad can argue he is yet another victim if U.S. aggression. Absent a coalition, sovereign governments will conclude the U.S. is undertaking actions for selfish but unstated reasons. If the U.S. should take action prior to forming a credible coalition, it will be nearly impossible to form one after the fact.
Forming a credible coalition may be the most important and most difficult step in a policy process like this one. The natural interest of most governments will be to lay low, letting the U.S.-led coalition conduct action while benefiting from any success, but reserving the right to criticize any unintended consequences. By remaining neutral governments can also avoid running afoul of segments of their population who may sympathize with whomever the U.S. is targeting. Potential partners must consider the risks of putting their name on the list. Islamic governments must consider the consequences for their long-term regional relationships should U.S.-led military action not succeed, or tactical errors with strategic consequences occur and shift the world’s animosity toward the coalition.
Therefore the United States has to take due diligence to build a strong logical case that persuades partner governments to sign up. The case must persuade a critical mass of international partners that the objective is necessary and desirable, it can be achieved with proposed actions, and that the costs of in-action outweigh the risks of action.