Wider war in the Mideast threatens. It can also be contained.

The drumbeat of escalation is getting louder, and the warnings more urgent, as the Middle East braces for the prospect of its worst war in half a century.

But a different kind of struggle – facing the leaders of all the major rivals – will determine when, and indeed whether, the 10-month-long conflict in Gaza expands to engulf the wider Mideast.

It might best be described as a contest between right brain and left brain, a hot swirl of emotions set against a cold, hard reality that all the combatants understand: In a full-scale war pitting Israel not just against Hamas in Gaza, but Iranian-armed Hezbollah in Lebanon, and Iran itself, all will pay heavily.

And none can, in any meaningful sense, expect to win. 

It’s a reality Washington and key allies have been striving to drive home in their effort to keep the latest round of tit-for-tat violence from plunging the region into its most serious multifront conflict since the Arab-Israeli war of 1973.

And while U.S., European, and Arab governments now seem to accept a major escalation as inevitable in the coming days, they still hope a recognition of the huge costs for all sides in an all-out war will allow it to be contained and gradually dialed back.

That’s what happened three-and-a-half months ago, the last time the region seemed on the brink of war.

An Israeli airstrike had killed senior officers in an Iranian embassy compound in Syria, and Tehran retaliated with its first direct attack on Israel.

Yet Iran publicly telegraphed its timing, Washington coordinated with Arab allies to help shoot down dozens of missiles and drones, and Israel responded with a single strike on an air-defense installation in Iran a few days later.

This time, the potential catalyst is more dramatic: Israel’s assassination of a Hezbollah commander in the Lebanese capital of Beirut, followed by the killing in Tehran of Hamas’ political leader and main cease-fire negotiator, Ismail Haniyeh, who was attending the inauguration of Iran’s new president.

And raw emotion now seems to be driving the leaders of Iran, Hezbollah, and Israel – reinforced by an apparent belief that a show of military force makes political sense as well.

Israeli Prime Minister Benjamin Netanyahu’s defiant response to the prospect of a two-front war with Iran and Hezbollah has, for now, muted growing protests over his failure to prevent Hamas’ cross-border attack of Oct. 7, its killing and abduction of hundreds of Israelis, and his rejection of a U.S.-backed deal for a Gaza cease-fire to recover dozens of Israeli hostages that Hamas still holds.

Iran’s supreme leader, Ayatollah Ali Khamenei, and his top military leaders are also determined to make Israel pay for Mr. Haniyeh’s death, and to expunge the political humiliation of failing to keep him safe during a major state occasion in Tehran.

Hezbollah leader Hassan Nasrallah seems equally intent on a significant military response to the killing of one of his top advisers, Fouad Shukur, especially since he was targeted in a densely populated southern suburb of the Lebanese capital.

The harsh reality of what full-scale war would mean, however, is what the U.S. and its Arab allies still hope will allow for this latest crisis to be contained.

The costs for Israel

The potential costs for Israel? Having already found that despite the huge scale of destruction and nearly 40,000 deaths in Gaza since Oct. 7, it has been unable to achieve the “total defeat” Mr. Netanyahu vowed to inflict on Hamas.

A wider war would be incomparably harder.

A sustained conflict with Iran could tax even Israel’s highly effective air defenses. That’s especially true given the likelihood that Washington would find it increasingly difficult to enlist Arab allies, angered over Israel’s conduct in Gaza, to help as they did in April’s Iranian missile attack.

And Hezbollah would present an even greater threat. Massed across Israel’s northern border, it is a far larger and better equipped force than Hamas. It has some 150,000 missiles, many of them precision-guided and capable of hitting anywhere in Israel.

Hezbollah’s calculus – and Iran’s

Hezbollah, too, knows the cost of an all-out war: almost certainly, Israeli strikes deep into Lebanon, including Beirut itself, targeting key national infrastructure, and inflicting huge damage and high casualties. The last such war was nearly two decades ago, a conflict neither side won and that Mr. Nasrallah later said that he came to regret.

Finally, Iran. Its Middle East strategy has been built around a self-styled “Axis of Resistance.” That network of allies and proxies, which includes Hamas, militia groups in Iraq and Syria, Houthi forces in Yemen and, above all Hezbollah, holds political sway in those countries and in effect encircles Israel without the need for Iran to risk direct military involvement.

An all-out war with Israel could risk all of that, beyond the likely damage that Israeli airstrikes would do to Iran’s infrastructure and its already struggling economy.

Washington’s deep concern remains that an angry churn of emotions and domestic political calculations may still win the day, and that a spiral of attack and counterattack will take on a momentum that proves impossible to halt.

Yet the U.S. hope remains that the left brain will trump the right brain: that cooler judgment will bring all sides to stop short of all-out war.