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With Donald Trump’s decision to shred the Iran nuclear agreement, announced last Tuesday, it’s time for the rest of us to start thinking about what a Third Gulf War would mean. The answer, based on the past 16 years of American experience in the Greater Middle East, is that it won’t be pretty.

The New York Times recently reported that US Army Special Forces were secretly aiding the Saudi Arabian military against Iranian-backed Houthi rebels in Yemen. It was only the latest sign preceding President Trump’s Iran announcement that Washington was gearing up for the possibility of another interstate war in the Persian Gulf region. The first two Gulf wars—Operation Desert Storm (the 1991 campaign to drive Iraqi forces out of Kuwait) and the 2003 US invasion of Iraq—ended in American “victories” that unleashed virulent strains of terrorism like ISIS, uprooted millions, and unsettled the Greater Middle East in disastrous ways. The Third Gulf War—not against Iraq but Iran and its allies—will undoubtedly result in another American “victory” that could loose even more horrific forces of chaos and bloodshed.

Like the first two Gulf wars, the third could involve high-intensity clashes between an array of American forces and those of Iran, another well-armed state. While the United States has been fighting ISIS and other terrorist entities in the Middle East and elsewhere in recent years, such warfare bears little relation to engaging a modern state determined to defend its sovereign territory with professional armed forces that have the will, if not necessarily the wherewithal, to counter major US weapons systems.

A Third Gulf War would distinguish itself from recent Middle Eastern conflicts by the geographic span of the fighting and the number of major actors that might become involved. In all likelihood, the field of battle would stretch from the shores of the Mediterranean, where Lebanon abuts Israel, to the Strait of Hormuz, where the Persian Gulf empties into the Indian Ocean. Participants could include, on one side, Iran, the regime of Bashar al-Assad in Syria, Hezbollah in Lebanon, and assorted Shiite militias in Iraq and Yemen; and, on the other, Israel, Saudi Arabia, the United States, and the United Arab Emirates (UAE). If the fighting in Syria were to get out of hand, Russian forces could even become involved.

All of these forces have been equipping themselves with massive arrays of modern weaponry in recent years, ensuring that any fighting will be intense, bloody, and horrifically destructive. Iran has been acquiring an assortment of modern weapons from Russia and possesses its own substantial arms industry. It, in turn, has been supplying the Assad regime with modern arms and is suspected of shipping an array of missiles and other munitions to Hezbollah. Israel, Saudi Arabia, and the UAE have long been major recipients of tens of billions of dollars of sophisticated American weaponry, and President Trump has promised to supply them with much more.

This means that, once ignited, a Third Gulf War could quickly escalate and would undoubtedly generate large numbers of civilian and military casualties, as well as new flows of refugees. The United States and its allies would try to quickly cripple Iran’s war-making capabilities, a task that would require multiple waves of air and missile strikes, some surely directed at facilities in densely populated areas. Iran and its allies would seek to respond by attacking high-value targets in Israel and Saudi Arabia, including cities and oil facilities. Iran’s Shiite allies in Iraq, Yemen, and elsewhere could be expected to launch attacks of their own on the US-led alliance. Where all this would lead, once such fighting began, is of course impossible to predict, but the history of the 21st century suggests that, whatever happens, it won’t follow the carefully laid plans of commanding generals (or their civilian overseers) and won’t end either expectably or well.

Precisely what kind of incident or series of events would ignite a war of this sort is similarly unpredictable. Nonetheless, it seems obvious that the world is moving ever closer to a moment when the right (or perhaps the better word is wrong) spark could set off a chain of events leading to full-scale hostilities in the Middle East in the wake of President Trump’s recent rejection of the nuclear deal. It’s possible, for instance, to imagine a clash between Israeli and Iranian military contingents in Syria sparking such a conflict. The Iranians, it is claimed, have set up bases there both to support the Assad regime and to funnel arms to Hezbollah in Lebanon. On May 10, Israeli jets struck several such sites, following a missile barrage on the Israeli-occupied Golan Heights said to have been launched by Iranian soldiers in Syria. More Israeli strikes certainly lie in our future as Iran presses its drive to establish and control a so-called land bridge through Iraq and Syria to Lebanon. Another possible spark could involve collisions or other incidents between American and Iranian naval vessels in the Persian Gulf, where the two navies frequently approach each other in an aggressive manner. Whatever the nature of the initial clash, rapid escalation to full-scale hostilities could occur with very little warning.

All of this begs a question: Why are the United States and its allies in the region moving ever closer to another major war in the Persian Gulf? Why now?

The Geopolitical Impulse

The first two Gulf wars were driven, to a large extent, by the geopolitics of oil. After World War II, as the United States became increasingly dependent on imported sources of petroleum, it drew ever closer to Saudi Arabia, the world’s leading oil producer. Under the Carter Doctrine of January 1980, the US pledged for the first time to use force, if necessary, to prevent any interruption in the flow of oil from Saudi Arabia and other Gulf states to this country and its allies. Ronald Reagan, the first president to implement that doctrine, authorized the “reflagging” of Saudi and Kuwaiti oil tankers with the Stars and Stripes during the eight-year Iran-Iraq War that began in 1980, as well as their protection by the US Navy. When Iranian gunboats menaced such tankers, American vessels drove them off in incidents that represented the first actual military clashes between the United States and Iran. At the time, President Reagan put the matter in no uncertain terms: “The use of the sea lanes of the Persian Gulf will not be dictated by the Iranians.”

Oil geopolitics also figured prominently in the US decision to intervene in the First Gulf War. When Iraqi forces occupied Kuwait in August 1990 and appeared poised to invade Saudi Arabia, President George H.W. Bush announced that the US would send forces to defend the kingdom and so played out the Carter Doctrine in real time. “Our country now imports nearly half the oil it consumes and could face a major threat to its economic independence,” he declared, adding that “the sovereign independence of Saudi Arabia is of vital interest to the United States.”

Although the oil dimension of US strategy was less obvious in President George W. Bush’s decision to invade Iraq in March 2003, it was still there. Members of his inner circle, especially Vice President Dick Cheney, argued that Iraqi ruler Saddam Hussein posed a threat to the safety of Persian Gulf oil lanes and needed to be eliminated. Others in the administration were eager to pursue the prospect of privatizing Iraq’s state-owned oil fields and turning them over to American oil companies (a notion that evidently stuck in Donald Trump’s mind, as he repeatedly asserted during the 2016 election campaign that “we should have kept the oil”).

Today, oil has receded, if not entirely disappeared, as a major factor in Persian Gulf geopolitics, while other issues have moved to the fore. Of greatest significance in animating the current military standoff is an escalating struggle for regional dominance between Iran and Saudi Arabia (with a nuclear-armed Israel lurking in the wings). Both countries view themselves as the hub of a network of like-minded states and societies—Iran as the leader of the region’s Shiite populations, Saudi Arabia of its Sunnis—and each resents any gains by the other. To complicate matters, President Trump, clearly harboring deep antipathy toward the Iranians, has chosen to side with the Saudis big league (as he might say), while Benjamin Netanyahu’s Israel, fearing Iranian advances in the region, has opted to weigh in on the Saudi side of the equation in a major way as well. The result, as suggested by military historian Andrew Bacevich, is the “inauguration of a Saudi-American-Israeli axis” and a “major realignment of U.S. strategic relationships.”

Several key factors explain this transition from an oil-centric strategy emphasizing military power to a more conventional struggle among regional rivals that has already deeply embroiled the planet’s last superpower. To begin with, America’s reliance on imported oil has diminished rapidly in recent years, thanks to an oil-drilling revolution in the US that has allowed the massive exploitation of domestic shale reserves through the process of fracking. As a result, access to Persian Gulf supplies matters far less in Washington than it did in previous decades. In 2001, according to oil giant BP, the United States relied on imports for 61 percent of its net oil consumption; by 2016, that share had dropped to 37 percent and was still falling—and yet the US remains deeply involved in the region as a decade and a half of unending war, counterinsurgency, drone strikes, and other kinds of strife sadly indicate.

By invading and occupying Iraq in 2003, Washington also eliminated a major bulwark of Sunni power, a country led by Saddam Hussein, who, two decades earlier, had been siding with the US in opposing Iran. That invasion, ironically enough, had the effect of expanding Shiite influence and making Iran the major—possibly the only—winner in the years of war that followed. Some Western analysts believe that the greatest tragedy of the invasion, from a geopolitical point of view, was the ascent of Shiite politicians with close ties to Tehran in post-Hussein Iraq. Although that country’s current leaders appear intent on pursuing a path of their own in the post-ISIS moment, many powerful Iraqi Shiite militias—including some that played key roles in driving Islamic State militants out of Mosul and other major cities—retain close ties to Iran’s Revolutionary Guards.

While disasters in themselves, the wars in Syria and Yemen have only added additional complexity to the geopolitical chessboard on which Washington found itself after that invasion and from which it has never extricated itself. In Syria, Iran has chosen to ally with Vladimir Putin’s Russia to preserve the brutal Assad regime, providing it with arms, funds, and an unknown number of advisers from the Revolutionary Guards. Hezbollah, a Shiite political group in Lebanon with a significant military wing, has sent large numbers of its own fighters to Syria to help Assad’s forces. In Yemen, the Iranians are believed to be providing arms and missile technology to the Houthis, a homegrown Shiite rebel group that now controls the northern half of the country, including the capital, Sanaa.

The Saudis, in turn, have been playing an ever more active role in bolstering their military power and protecting embattled Sunni communities throughout the region. Seeking to resist and reverse what they view as Iranian advances, they have helped arm militias of an extreme sort and evidently even Al Qaeda–associated groups under attack from Iranian-backed Shiite forces in Iraq and Syria. In 2015, in the case of Yemen, they organized a coalition of Sunni Arab states to crush the Houthi rebels in a brutal war that has included a blockade of the country, helping to produce mass famine, and a relentless American-backed air campaign, which often hits civilian targets including markets, schools, and weddings. This combination has helped produce an estimated 10,000 civilian deaths and a humanitarian crisis in that already impoverished country.

In response to these developments, the Obama administration sought to calm the situation by negotiating a nuclear deal with the Iranians and by holding out the promise of increased economic ties with the West in return for Iran’s reduced assertiveness outside its borders. Such a strategy, however, never won the support of Israel or Saudi Arabia. And in the Obama years, Washington continued to support both of those countries in a major way, including supplying massive amounts of military equipment, refueling Saudi planes in midair so they could strike deeper into Yemen, and providing the Saudis with targeting intelligence for their disastrous war.

The Anti-Iranian Triumvirate

All of these regional developments, in play before Donald Trump was elected, have only gained added momentum since then, thanks in no small degree to the pivotal personalities involved.

The first of them, of course, is President Trump. Throughout his election campaign, he regularly denounced the nuclear deal that Iran, the United States, Britain, France, Germany, Russia, China, and the European Union all signed onto in July 2015. Officially known as the Joint Comprehensive Plan of Action (JCPOA), the agreement forced Iran to suspend its uranium-enrichment program in return for the lifting of all nuclear-related sanctions. It was a plan that Iran scrupulously adhered to. Although President Obama, many senior American policymakers, and most European leaders had argued that the JCPOA—whatever its flaws—provided a valuable constraint on Iran’s nuclear (and so other) ambitions, Trump consistently denounced it as a “terrible deal” because it failed to eliminate every last vestige of the Iranian nuclear infrastructure or ban that country’s missile program. “This deal was a disaster,” he told David Sanger of The New York Times in March 2016.

While Trump, who has filled his administration with Iranophobes, including his new secretary of state and new national-security adviser, seems to harbor a primeval animosity toward the Iranians, perhaps because they don’t treat him with the adoration he feels he deserves, he has a soft spot for the Saudi royals, who do. In May 2017, on his first trip abroad as president, he traveled to Riyadh, where he performed a sword dance with Saudi princes and immersed himself in the sort of ostentatious displays of wealth only oil potentates can provide.

While in Riyadh, he conferred at length with then–Deputy Crown Prince Mohammed bin Salman, the 31-year-old son of King Salman and a key architect of Saudi Arabia’s geopolitical contest with the Iranians. Prince Mohammed, who serves as the Saudi defense minister and was named crown prince in June 2017, is the prime mover behind the kingdom’s (so far unsuccessful) drive to crush the Houthi rebels in Yemen and is known to harbor fierce anti-Iranian views.

At an earlier White House luncheon in March 2017, Salman, or MBS as he’s sometimes known, and President Trump seemed to reach an implicit agreement on a common strategy for branding Iran a regional threat, tearing up the nuclear agreement, and so setting the stage for an eventual war to vanquish that country or at least to fell the regime that runs it. While in Riyadh, President Trump told a conference of Sunni Arab leaders that, “from Lebanon to Iraq to Yemen, Iran funds, arms, and trains terrorists, militias, and other extremist groups that spread destruction and chaos across the region. It is a government that speaks openly of mass murder, vowing the destruction of Israel, death of America, and ruin for many leaders and nations in this very room.”

While no doubt gratifying to the Saudis, Emiratis, Kuwaitis, and other Sunni rulers listening, those words echoed the views of the third key player in the strategic triumvirate that may soon drive the region into all-out war, Israeli Prime Minister Benjamin Netanyahu, also known as “Bibi.” For years, he has railed against Iranian ambitions in the region and threatened military action against any Iranian move that would, as he saw it, impinge on Israeli security. Now, in Trump and the Saudi crown prince, he has the allies of his dreams. In the Obama years, Netanyahu was a fierce opponent of the Iranian nuclear deal and used a rare appearance before a joint session of Congress in March 2015 to denounce it in no uncertain terms. He has never—right up to the days before Trump withdrew from the accord—stopped working to persuade the president that the agreement should be junked and Iran targeted.

In that 2015 speech to Congress, Netanyahu laid out a vision of Iran as a systemic danger that would later be appropriated by Trump and his Saudi confederates in Riyadh. “Iran’s regime poses a grave threat, not only to Israel, but also the peace of the entire world,” he asserted in a typically hyperbolic statement. “Backed by Iran, Assad is slaughtering Syrians. Backed by Iran, Shiite militias are rampaging through Iraq. Backed by Iran, Houthis are seizing control of Yemen, threatening the strategic strait at the mouth of the Red Sea. Along with the Straits of Hormuz, that would give Iran a second choke-point on the world’s oil supply.”

Now Netanyahu is playing a major role in driving the already crippled region into a war that could further destroy it, produce yet more terror groups (and terrorized civilians), and create havoc on a potentially global scale, given that both Russia and China back the Iranians.

Girding for War

Pay attention to the words of Netanyahu in Washington and Donald Trump in Riyadh. Think of them not as political rhetoric, but as prophecies of a grim kind. You’re going to be hearing a lot more such prophecies in the months ahead as the United States, Israel, and Saudi Arabia move closer to war with Iran and its allies. While ideology and religion will play a part in what follows, the underlying impetus is a geopolitical struggle for control of the greater Persian Gulf region, with all its riches, between two sets of countries, each determined to prevail.

No one can say with certainty when, or even if, these powerful forces will produce a devastating new war or set of wars in the Middle East. Other considerations—an unexpected flare-up on the Korean Peninsula if President Trump’s talks with North Korea’s Kim Jong-un end in failure, a fresh crisis with Russia, a global economic meltdown—could turn attention elsewhere, lessening the importance of the geopolitical contest in the Persian Gulf. New leadership in any of the key countries could similarly lead to a change of course. Netanyahu, for example, is now at risk of losing power because of an ongoing Israeli police investigation into allegedly corrupt acts of his, and Trump, well, who can say? Without such a development or developments, however, the way to war, which will surely prove to be the road to hell, seems open with a Third Gulf War looming on humanity’s horizon.