Days before the U.S.-led forces invaded Afghanistan to avenge the attacks on 9/11, President George W. Bush outlined   his   approach to the Global War on Terror (GWOT): “Our war on terror begins with al-Qaeda, but it does not end there.” What followed was a worldwide co - alition, led by the United States, whose primary objective was to “destroy al-Qaeda’s grip on Afghanistan by driving the Taliban from power.” Twenty years later, on August 15, 2021, the Taliban returned to power in Afghanistan. A week later the Pentagon   contradicted the state - ment of U.S. President Joe Biden and acknow - ledged that al-Qaeda was not completely eradicated from Afghanistan. One of the more important factors behind the U.S. setback against al-Qaeda in Afghanistan – and perhaps the war in Afghanistan more generally – is Iran’s exclusion from this Global War on Terror. Iran’s exclusion was a lost opportunity, missed on two notable occasions: first, during the fight against al-Qaeda in 2001; and second, when a coalition was built in 2014 to fight against the Islamic State of Iraq and Syria (ISIS). The U.S. policy of isolating Iran has not only led to the augmentation of Shiʿa extremism but also indirectly fueled Sunni extremist forces. When the U.S.-led coalition started its operations against Afghanistan, Iran provided “ critical assistance ,” including military and intelligence cooperation. Iran even provided diplomatic support in the efforts to establish a new government in Afghanistan through the 2001 Bonn Conference. But such cooperation was short-lived due to George W. Bush’s pronouncement that Iran was a part of the “Axis of Evil.” The start of Iran’s nuclear controversy in August 2002 also adversely impacted U.S.-Iran cooperation. As early as September 2003, The Washington Post reported that “after the fall of the Taliban in Afghanistan, the locus of al- Qaeda’s degraded leadership moved to Iran.” It is also believed that “Iran likely opened up communications with al-Qaeda in 2004 due to al-Zarqawi’s targeting of Shiite holy sites in Iraq.” In recent years, Iran’s ties with al-Qaeda were highlighted   by The New York Times in its 2020 report that al-Qaeda’s Abu Muhammad al-Masri – believed to be the “ next    in    line    to    lead    al- Qaida ” – was secretly killed in Tehran. Iran officially dismissed this report and “strongly denied any presence of the terrorist group’s members in Iran.” This denial ran contrary to the claim   of U.S. Secretary of State Mike Pompeo, who claimed in early 2021 that al-Masri was shot dead in Iran the previous year. Pompeo also claimed that “al-Qaida has a new home base: it is the Islamic Republic of Iran.” It is of note that such comments were made days before Pompeo was about to leave office and are evidently in line with the efforts of President Trump’s administration to pre-empt Biden’s stated objective of resurrecting the Joint Comprehensive Plan of Action (JCPOA). Nonetheless, following al-Masri’s death, The Washington Post reported that “the only remaining member of al-Qaeda’s shura council — its core leadership — with operational al- Qaeda terrorist experience is Saif al-Adel, who is believed still to be in Iran,” raising the prospect that an axis between Iran and al-Qaeda remained intact. While one finds ample    controversy over the relationship between Iran and al-Qaeda, there is no such controversy between Iran and ISIS. Iran and ISIS are bitter enemies and there is little evidence to suggest that the two have linkages of any kind. Still, when ISIS declared a Caliphate and an international conference was held in Paris on September 15, 2014 by the leaders of over 30 countries to discuss the modalities of countering ISIS, Iran was deliberately excluded from this forum. Nevertheless, there was some tacit cooperation between Iran and the U.S. in their fight against ISIS, exemplified by U.S. air support for Iranian- backed Shiʿa militias in Iraq seeking to reverse ISIS advances. Iran also reportedly sent its Quds commander to Iraq in order to safeguard the country’s Shiʿa Muslims and adopted “an interventionist approach in Iraq and Syria, largely through the use of allied militias, including a largely Afghan Hazara group called the Fatemiyoun.” While U.S. President Barack Obama favored a strategy of strengthening moderate opposition forces in Syria to fight both ISIS and Syrian President Bashar al-Assad, Iran favoured the survival of al-Assad’s regime and looked at the U.S. strategy with suspicion. Moreover, the global coalition against ISIS included many Arab countries; the U.S. feared that Iran’s inclusion could have resulted in the abstention of Saudi Arabia and the United Arab Emirates. President Obama may have further calculated that including Iran in a coalition against ISIS could have jeopardized its bargaining position in nuclear negotiations, opposed by U.S. regional ally Israel. One year after the Taliban’s return to power in Afghanistan, it is widely perceived that “al-Qaeda is regrouping and remains intent on becoming the leader of the global jihadist movement.” Al- Qaeda has certainly demonstrated that it has “learned the secret of longevity.” Moreover, President Biden’s administration is still   engaged in the fight against ISIS. If the U.S. and Iran could work on some modalities to cooperate in this regard, perhaps the challenges of Sunni extremism could have been tackled more expediently. The U.S. policy of isolation has not necessarily led to the depletion of Iranian power or its geostrategic reach. The standoff over Iran’s nuclear program also resulted in an acceleration of its nuclear enrichment. U.S.-led sanctions have brought Iran closer to the two primary foes of U.S. power: Russia, and China. After four decades of rivalry with the United States, Iran has certainly devised a strategy to fight its enemies far away from its borders. Iran’s regional proxies are part of that strategy. Notably, Iran’s proxies are not confined to Shiʿa groups, but include Sunni groups as well, such as Hamas. Under an environment wherein Iran and the U.S. continue to nourish their enmity, Iran’s asymmetric power and compulsion of hedging may cause it to widen the fold of its proxies. One must wonder whether some elements of the U.S.-Iran rivalry might have been more easily resolved if that country had been brought on board in the Global War on Terror.