Jim Hoagland is a contributing editor to The Post. His e-mail address is jimhoagland@washpost.com.

Syria’s civil war is the decisive event in the remaking of the Middle East that began with the self-immolation of a Tunisian fruit vendor 21 months ago. The battle for Damascus has become the fulcrum of a now fully visible Sunni-Shiite struggle over the creation and control of an Islamic political order throughout the region.

The Pax Americana that has prevailed in the region since 1973 — the last time a major Arab-Israeli war erupted — is rapidly eroding. American power, friendship or enmity will no longer be decisive for Egyptians, Syrians or even Saudis in the ways they have been for nearly four decades.

The Sunnis of Saudi Arabia and other gulf nations are putting all their chips on the effort to bring down Bashar al-Assad’s regime in Damascus and inflict a strategic defeat on Assad’s Shiite allies in Tehran. The crumbling of Assad’s rule will soon force the Iranians to go all in as well — or accept the humiliation of their surrogate’s downfall.

An Iranian decision to escalate to save Assad, perhaps by retaliating against the gulf Arabs, would push the burden back on the Obama administration — in the middle of a heated presidential campaign — to define and protect U.S. regional interests more clearly and decisively.

President Obama’s country-by-country, tactical responses to this unfolding Arab revolt have, until now, served the United States fairly well. But the strategic struggle between the gulf Arabs and Iran in Syria unhorses that narrow, reactive approach.

Several large caveats must be acknowledged in this analysis: There has, of course, been turmoil aplenty in the strategic crossroads of Asia and Africa since Henry Kissinger committed U.S. power to brokering the 1973 Arab-Israeli truce that grew into an Egyptian-Israeli peace treaty. But the subsequent wars in Lebanon, Yemen, Iraqi Kurdistan, Kuwait, and even between Iran and Iraq were contained within the contours of a U.S.-supported equilibrium. Pax imperfect, yes, but pax at a regional level nonetheless.

Second, this is not to say that the United States suddenly lacks influence or interests in the Middle East. On the contrary. It will fall to a reelected Obama or a newly installed Mitt Romney to shift U.S. diplomacy and security policies in the Middle East back onto a regional scale — one less dependent on traditional national instruments of power and less protective of the post-colonial Arab secular state system that is being atomized.

By focusing on democracy, territorial integrity and human rights as U.S. goals to be achieved one country at a time, the Obama administration has deliberately minimized the religious roots and regional nature of the broader Sunni-Shiite conflict. But for its protagonists, the war turns on the Sunni majority’s right to rule in Syria and on weakening Shiite power in Tehran and Baghdad.

The objectives sought by the United States and the gulf Arabs are thus misaligned. As long as that is the case, direct U.S. military intervention in Syria to help the rebels win will continue to be a matter of last resort.

This does not mean accepting or supporting the inhumane status quo. Turmoil on this scale can produce territorial breakups that relieve pressures instead of intensifying them. (The Soviet Union and Yugoslavia provide recent examples.) U.S. policy should be nimble enough to facilitate border changes that would provide more protection for ethnic or religious minorities in Syria, Iraq or elsewhere.

Another conceptual change will involve the loss of U.S. influence in Egypt, which can no longer serve as the linchpin of U.S. regional policy. American interests are centered as never before in the gulf Arab nations. U.S. policy must follow that shift.

That means actively engaging in efforts to bolster friendly governments — it is time to revive discussions held in the Bush 43 administration about extending some form of a nuclear umbrella to gulf allies — while encouraging them to drop ancient, self-defeating national prejudices about religion, gender and minorities in return for a new relationship with Washington.

Egypt provides a good example of how to begin this shifting of gears. Freeing important sectors of the Egyptian economy from the monopolistic control of the military — the national instrument the United States has relied on most heavily to exert influence there — could spark a much-needed economic rebound. U.S. experts, business people and generals could help in a transition that would have the added benefit of the Egyptian military, and U.S. security assistance, being downsized.

Crisis of this magnitude always creates the need for new thinking. Only imaginative, aware minds can create the thinking itself.