"The regional adjustment has begun," writes Kagan. "Gulf rulers who once counted on an American security guarantee must now make their peace with the power that proved capable of defeating their protector."

Saudi Arabia's rejection of the U.S.- and Israel-backed Abraham Accords in favor of a strategic compact with Pakistan and Turkey hints at the shape of the future. The Abraham Accords represented the consolidation of Israeli power and influence in the region and the further containment of Iran. The Mecca pact is something else entirely. Neither Pakistan nor Turkey regards Iran as a major threat; Pakistan, like Iran, has close relations with China; Israel regards Turkey as a regional threat second only to Iran. Instead of an American-Israeli order, this will be an alignment less implacably hostile to Iran, less friendly to Israel, and more independent of the United States. The signatories also have nuclear weapons in common: Pakistan has them, and the Turks and Saudis want them.

"The effects will extend far beyond the Middle East," Kagan believes.

American allies in Asia and Europe can see that a relatively brief war against a second-rank power has consumed much of America's supply of the weapons needed for missile defense. They can see that the United States began a war it could not finish, exposed its partners to retaliation, and then stopped when the costs became too great. Beijing's conclusions about Taiwan, and Moscow's conclusions about Europe, may be impossible to know. But America's allies will inevitably be asking whether Washington has the weapons, stamina, and political will to sustain another major conflict. In fact, they already are.