Afghanistan and Pakistan are two of the only countries where prominent branches of all three major Islamic terrorist organizations coexist. And the rise of the so-called Islamic State in the two areas could prompt a merger between two of the oldest and most dangerous terrorist organizations to counter the militant group. Al Qaeda and the Taliban have always been loosely alligned, but as ISIS advances across the region, a solid unified front between the two is essential to maintaining their presence in certain areas.  

The group also known as ISIS has been active in both Afghanistan and Pakistan since 2014 and, despite backlash from the Afghan government and Afghan Taliban forces present in the area, it has been able to expand. The Taliban suffered losses from both ISIS gains and the announcement of the death of its leader Mullah Mohammad Omar. But the insurgent group’s reputation will get a significant boost after Thursday’s pledge of allegiance from the head of al Qaeda Ayman al-Zawahiri.

"As emir of al-Qaeda, I pledge to you our allegiance, following the path of Sheikh (Osama) bin Laden and his martyred brothers in their allegiance to Mullah Omar,” Zawahiri said in an apparent voice recording released by al Qaeda’s al-Sahab media wing, according to the BBC.

Mullah Omar Mullah Omar, leader of the Taliban. Photo: Getty Images

The pledge of allegiance came just weeks after the Taliban announced that Omar had been killed in Pakistan in 2013. Most Islamic militant groups, with the exception of ISIS, considered Omar the leader of the global jihadist movement.

Omar’s replacement, Mullah Akhtar Mansour, was not accepted by some prominent Taliban leaders and certain al Qaeda branches across the region. However,  Zawahiri’s pledge of allegiance to Mansour could help legitimize the new leader and unite the two organizations.

“We are your soldiers and your supporters and a brigade of your brigades,” Zawahiri said in a message disseminated over social media and translated by the SITE Intelligence Group.

ISIS had hoped to use the recent disunity to encourage defections from the Taliban and al Qaeda. However, an alliance between the two groups could slow ISIS’ progress in Afghanistan, where it has been recruiting fighters and seizing the Taliban’s territory.

In January, ISIS declared the so-called Wilayat Khorasan, a new militant province comprised of parts of Afghanistan and Pakistan. At least five of its 12 appointed leaders were former members of Tehreek e-Taliban e-Pakistan, the Pakistani branch of the Taliban who had defected from the group in October. By June, ISIS had managed to seize “substantial territory” in areas of Afghanistan formerly controlled by the Taliban, according to an exclusive report from Reuters.

The militant group is not yet able to coordinate military attacks within the country, but it is growing into "something more serious, more dangerous," U.S. Army Brig. Gen. Wilson Shoffner told Pentagon reporters from his office in Kabul on Thursday.