Deadly terrorist attacks in Istanbul, Dhaka, and Baghdad demonstrate the murderous reach of the Islamic State group in Europe, North Africa, the Middle East, and parts of Asia. The longer IS maintains its strongholds in Syria and Iraq, the longer its terrorist network will create such carnage. Yet IS is not especially difficult to defeat. The problem is that none of the states involved in Iraq and Syria, including the United States and its allies, has so far treated IS as its primary foe. It is time they do.

IS has a small fighting force, which the U.S. puts at 20,000 to 25,000 in Iraq and Syria, and another 5,000 or so in Libya. Compared to the number of active military personnel in Syria (125,000), Iraq (271,500), Saudi Arabia (233,500), Turkey (510,600), or Iran (523,000), IS is minuscule.

Despite U.S. President Barack Obama’s pledge in September 2014 to “degrade and ultimately destroy” IS, the U.S. and its allies, including Saudi Arabia, Turkey, and Israel (behind the scenes), have been focusing instead on toppling Syria’s Bashar al-Assad.

Consider a recent candid statement by Israeli Maj. Gen. Herzi Halevy (quoted to me by a journalist who attended the speech where Halevy made it): “Israel does not want to see the situation in Syria end with (IS) defeated, the superpowers gone from the region, and (Israel) left with a Hezbollah and Iran that have greater capabilities.”

Israel opposes IS, but Israel’s greater concern is Assad’s Iranian backing. Assad enables Iran to support two paramilitary foes of Israel, Hezbollah and Hamas. Israel therefore prioritizes the removal of Assad over the defeat of IS.

For the U.S., steered by neoconservatives, the war in Syria is a continuation of the plan for global U.S. hegemony launched by Defense Secretary Richard Cheney and Undersecretary Paul Wolfowitz at the Cold War’s end. In 1991, Wolfowitz told U.S. Gen. Wesley Clark:

“But one thing we did learn (from the Persian Gulf War) is that we can use our military in the region -- in the Middle East -- and the Soviets won’t stop us. And we’ve got about 5 or 10 years to clean up those old Soviet regimes -- Syria, Iran (sic), Iraq -- before the next great superpower comes on to challenge us.”

The multiple U.S. wars in the Middle East -- Afghanistan, Iraq, Syria, Libya, and others -- have sought to remove the Soviet Union, and then Russia, from the scene and to give the U.S. hegemonic sway. These efforts have failed miserably.

For Saudi Arabia, as for Israel, the main goal is to oust Assad in order to weaken Iran. Syria is part of the extensive proxy war between Shia Iran and Sunni Saudi Arabia that plays out in the battlefields of Syria and Yemen and in bitter Shia-Sunni confrontations in Bahrain and other divided countries in the region (including Saudi Arabia itself).

For Turkey, the overthrow of Assad would bolster its regional standing. Yet Turkey now faces three foes on its southern border: Assad, IS, and nationalist Kurds. IS has so far taken a back seat to Turkey’s concerns about Assad and the Kurds. But IS-directed terrorist attacks in Turkey may be changing that.

Russia and Iran, too, have pursued their own regional interests, including through proxy wars and support for paramilitary operations. Yet both have signaled their readiness to cooperate with the U.S. to defeat IS, and perhaps to solve other problems as well. The U.S. has so far spurned these offers, because of its focus on toppling Assad.

The U.S. foreign-policy establishment blames Russian President Vladimir Putin for defending Assad, while Russia blames the U.S. for trying to overthrow him. These complaints might seem symmetrical, but they’re not. The attempt by the U.S. and its allies to overthrow Assad violates the U.N. Charter, while Russia’s support of Assad is consistent with Syria’s right of self-defense under that charter. Yes, Assad is a despot, but the U.N. Charter does not give license to any country to choose which despots to depose.

The persistence of IS underscores three strategic flaws in U.S. foreign policy, along with a fatal tactical flaw.

First, the neocon quest for U.S. hegemony through regime change is not only bloody-minded arrogance; it is classic imperial overreach. It has failed everywhere the U.S. has tried it. Syria and Libya are the latest examples.

Second, the CIA has long armed and trained Sunni jihadists through covert operations funded by Saudi Arabia. In turn, these jihadists gave birth to IS, which is a direct, if unanticipated, consequence of the policies pursued by the CIA and its Saudi partners.

Third, the U.S. perception of Iran and Russia as implacable foes of America is in many ways outdated and a self-fulfilling prophecy. A rapprochement with both countries is possible.

Fourth, on the tactical side, the U.S. attempt to fight a two-front war against both Assad and IS has failed. Whenever Assad has been weakened, Sunni jihadists, including IS and the Nusra Front, have filled the vacuum.

Assad and his Iraqi counterparts can defeat IS if the U.S., Russia, Saudi rabia, and Iran provide air cover and logistical support. Yes, Assad would remain in power; yes, Russia would retain an ally in Syria; and yes, Iran would have influence there. Terrorist attacks would no doubt continue, perhaps even in the name of IS for a while, but the group would be denied its base of operations in Syria and Iraq.

Such an outcome would not only end IS on the ground in the Middle East, it could lay the groundwork for reducing regional tensions more generally. The U.S. and Russia could begin to reverse their recent new cold war through shared efforts to stamp out jihadist terrorism. A pledge that NATO will not offer admission to Ukraine or escalate missile defenses in Eastern Europe would also help.

There is more. A cooperative approach to defeating IS would give Saudi Arabia and Turkey reason and opportunity to find a new modus vivendi with Iran. Israel’s security could be enhanced by bringing Iran into a cooperative economic and geopolitical relationship with the West, in turn enhancing the chances for a long-overdue two-state settlement with Palestine.

The rise of IS is a symptom of the shortcomings of current Western -- particularly U.S. -- strategy. The West can defeat IS. The question is whether the U.S. will undertake the strategic reassessment needed to accomplish that end.

By Jeffrey D. Sachs

Jeffrey D. Sachs is a professor of sustainable development, a professor of health policy and management, and the director of the Earth Institute at Columbia University. He is also the director of the U.N. Sustainable Development Solutions Network. -- Ed.

(Project Syndicate)