The US is getting out of Afghanistan, but it is unlikely to get out — and stay out — of the Middle East. For the past decade, three presidents have tried to downsize the American presence in the region; for generations, the Middle East has been a strategic morass. But the US seems stuck there, because its interests are challenged by three lasting crises. America’s core interests in the Middle East are straightforward. Persian Gulf oil still lubricates the global economy, even if the US itself doesn’t import much of it anymore. The region sits at the crossroads of three continents, which gives Washington further incentive to protect it from hostile powers. The US also seeks to prevent the Middle East from becoming a source of threats, whether nuclear-armed rogue states or catastrophic terrorism. Over the past 40 years, these interests have been imperiled by three interrelated trends. The first is the absence of any balance of power that can be preserved without US involvement. Britain’s withdrawal from “East of Suez” in the late 1960s meant the loss of a friendly power policing the region. The Iranian revolution in 1979 then turned the Gulf’s most powerful state into its chief source of instability. Alignments have since fluctuated: Iraq, for instance, has been a tacit American ally, then its primary enemy, and most recently a friendly if fragile state. But geopolitical upheaval has been the rule. The second trend is the upsurge of Islamist political movements, many of them hostile to Washington. This began after the Six-Day War of 1967, in which corrupt, secular Arab regimes were thumped by Israel. Critical breakthroughs came again in 1979. The Iranian revolution replaced a pro-Western monarchy with an anti-American theocracy that stimulated radicalism across the region. The Soviet invasion of Afghanistan triggered a furious reaction, one that America supported during the 1980s before later becoming one of its targets. Political Islam has subsequently come in many varieties, but it has often underpinned regimes and movements that challenge the US — sometimes violently. This touches on a third trend: the rise of terrorism as a tool of asymmetric warfare. After the revolution, the Iranian regime used terrorism aggressively to project power and attack stronger enemies. A growing number of extremist groups emulated the practice. Among their targets has been the US, in part because of the military presence it had built to protect the flow of oil and defend its other regional interests. The US, then, has confronted a tangle of threats over the past 40 years, and none of the many strategies it has tried has succeeded enough to allow it to safely disengage. In the 1980s, Washington supported Saddam Hussein’s Iraq as a bulwark against radical Iran, only to have Saddam become a greater threat to the region’s security. After 9/11, the US invaded Afghanistan and Iraq in hopes of transforming the Middle East geopolitically and ideologically. Instead, those actions, particularly the invasion of Iraq, further roiled the region. President Barack Obama then looked to lighten American burdens by withdrawing from Iraq and cutting a nuclear deal with Iran. But that stoked fears among Sunni states that Iran was headed for regional hegemony. It also facilitated the rise of ISIS, a terrorist super-state in the heart of the Middle East. By these standards, President Donald Trump’s incoherent approach — talking about ending “forever wars” while never quite doing so; expressing a desire to get out of the Middle East while provoking a dangerous confrontation with Iran — was about par for the course. Today, President Joe Biden is withdrawing from Afghanistan on the basis of reasonable calculations: The US faces greater challenges elsewhere, and its military involvement in Afghanistan has produced disappointing results. But getting out won’t ease the sources of instability in the larger region; it may, rather, exacerbate them. The Taliban’s extreme version of political Islam will get the boost that comes from conquering a country and defeating a superpower. The threat from terrorist groups will probably grow, as America’s ability to monitor and suppress that danger diminishes. The regional balance of power doesn’t look particularly stable, as Iran continues to spread its influence and inches toward a nuclear capability. And now America’s regional allies surely worry, after the fall of Kabul, about their patron’s reliability. All of which means that the next few years will bring no shortage of crises that require an ambivalent superpower’s attention. The root of American misery in the Middle East is that US interests there are real and the threats to them have proved fairly intractable. The irony of Biden’s policy is that it may sharpen that dilemma. Bloomberg