To judge from the debate at the United Nations, the international tussle over Syria pits a united Arab League and the Western democracies against a recalcitrant Russia, which is trying to prop up the doomed dictatorship of Bashar al-Assad. If only it were so simple.

In reality, the U.N. debate obscures what has become one of the most complex, volatile and momentous power struggles in the history of the Middle East — one in which Assad and Syrian opposition forces have become virtual pawns, and Russia and the United States bit players.

The central drama in Syria is now a sectarian showdown, one that has been gathering force around the region since the U.S. invasion of Iraq. Syria has precipitated a crucial test of strength between Sunnis and Shiites, and between Turkey and Iran. It has triggered existential crises for Palestinians, Kurds and the Shiite government of Iraq. For Russia and the United States, Syria means not a display of Security Council clout but a potentially devastating exhibition of weakness — one that could greatly diminish the standing of both in the region.

To sort through the larger stakes of this conflict, let’s start with the Persian Gulf states — led by Qatar — that have been pushing hardest for Arab League and Security Council action against the Assad regime. The emirates say their goal is Syrian democracy — but their motives are purely sectarian. Their target is not Assad but Iran, the Persian Shiite enemy of the Arab Sunni monarchies. Iran’s alliance with Syria, vital to its power in the Middle East, depends on a regime controlled by Assad’s minority Alawite sect, which is an offshoot of Shiite Islam.

The Arab emirates’ best ally against Iran is not the United States but the Turkish government of Recep Tayyip Erdogan, which is openly backing the Free Syrian Army. Erdogan, too, claims to be outraged by Assad’s brutality. But as a Sunni Islamist and the hugely ambitious leader of a rising power, he also perceives a strategic opportunity for Turkey to replace Iran as the preeminent outside influence in the former eastern provinces of the Ottoman Empire. Inside Syria, Turkey is pushing the Sunni Muslim Brotherhood; in neighboring Iraq, Turkey’s support for Sunni parties, and for the autonomous region of Kurdistan, is increasingly conspicuous.

That brings us to Nouri ­al-Maliki, the Shiite prime minister of Iraq and a man known for paranoid thinking even in the best of circumstances. Maliki has concluded that the Syrian conflict endangers the Shiite supremacy in Baghdad that has been his signature achievement. This fear, more than authoritarian impulses, has motivated Maliki’s crackdown on Sunni leaders — which has plunged Iraq into its own crisis. Turkey’s assertiveness and Maliki’s response, in turn, have prompted Iraqi Sunnis and Kurds to consider whether they should split off their own regions into separate mini-states — a move that looks much more feasible if Syria tilts toward Sunni rule.

Iran, of course, is fighting back. It has dispatched weapons and advisers to Syria, and it is pressing Maliki to open a corridor across Iraq to facilitate more material support. Maliki, I’m told, is resisting — for now, at least. But the lines of what could easily become a regional sectarian war are clearly drawn.

The Palestinian Hamas movement, ruler of the Gaza Strip, is having its own Syrian crisis. The shift of regional power has all but ruptured its supply link to Iran and forced its external leadership to flee Damascus. This has the effect of strengthening both Hamas’s Gaza-based leaders and the rival Fatah movement in the West Bank. And it means foreign patronage of Hamas could shift toward Erdogan’s Turkey, Egypt’s Muslim Brotherhood or even Jordan. In the meantime, Israel can watch with quiet satisfaction as its biggest enemies — Iran, Hamas and Assad — are sapped of strength.

The problem for prospective regional winners such as Israel and Turkey is that Assad may not go quickly. There is no sign that he or the Alawite leadership are willing to accept the exit strategies being discussed at the United Nations, with or without Russian support. For now the regime appears intent on fighting to the bitter end. With several Alawite-dominated elite divisions and plenty of tanks and artillery, Assad has the capacity to hold out for months; with continued Iranian and Russian help, that could stretch to years. Remember: The civil war in neighboring Lebanon lasted 14 years.

A quick Assad collapse will expose Russia to the loss of its Syrian naval base and residual Middle East influence. A prolonged fight will expose the critical weakness of the United States. With U.S. or NATO military intervention in Syria ruled out, President Obama’s decision to withdraw all U.S. troops from Iraq just as this crisis was mounting all but eliminated U.S. leverage.

American strategy now consists largely of public statements proclaiming Assad’s inevitable downfall — a bluff that, it is hoped, will sway Vladi­mir Putin and Assad’s generals. What if it doesn’t? We could see a Syrian war that widens and deepens — with an outcome well beyond the U.N. Security Council’s control.