The threat posed by the Islamic State has once again hit the headlines following the New Year's Day attack on a crowded street in New Orleans on Wednesday by a man who may have ties to the terrorist network.

Shamsud-Din Jabbar, a U.S.-born citizen who lived in Texas and an Army Veteran, drove a pickup truck with an ISIS flag into a crowd of people on Bourbon Street, killing at least 15 people and injuring dozens of others.

However, the FBI has not confirmed his direct "affiliation" or "association" with the infamous terrorist network which has been expanding across the globe in recent years, particularly in regions like the Sahel in Africa, despite the 2019 assertion that the terrorist network had been "defeated."

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"Claims of the Islamic State defeat, just like claims of the defeat of al Qaeda, are premature," Bill Roggio, senior fellow with the Foundation for Defense of Democracies and editor of the Long War Journal, told Fox News Digital. "These groups may have setbacks, but they're persistent. 

"The Islamic State poses a threat from Afghanistan. It has a significant network in Africa, particularly in the Sahel and in East Africa, in Somalia. And its network in Iraq and Syria persists," he added. 

While the FBI has not confirmed that the New Orleans attacker was directly involved in ISIS, reports have suggested he was apparently sympathetic to the terrorist network and "pledged allegiance to ISIS" in a series of videos posted to his Facebook page, according to The New York Times. 

The FBI has not yet released a motive for the attack, and Roggio explained that this incident is unlikely to indicate there is a "resurgence" of ISIS, though the security expert did highlight that increasingly the terrorist network is finding itself up against less resistance in areas where it was previously opposed. 

The 2021 withdrawal from Afghanistan and the fall of the Bashar al-Assad regime in Syria last month to the al Qaeda-derived organization dubbed Hay’at Tahrir al-Sham left security vacuums in the Middle East and South Asia – similar to what contributed to the rise of ISIS following the U.S. withdrawal from Iraq. Security experts have warned ISIS and other terrorist networks could use these power gaps. 

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ISIS-K – the regional affiliate of the terrorist group that originated in Iraq and Syria – garnered international attention in August 2021 when it attacked Afghans fleeing the Taliban takeover amid the U.S. withdrawal and used a suicide bombing to kill 13 American service members and some 170 Afghan civilians.

The Taliban takeover prompted concern that Afghanistan would become a safe haven for terrorists like Taliban allies al Qaeda, the Tehreek-e-Taliban Pakistan and other jihadi groups, though there was also concern that the new governing body in Afghanistan would be unable to oppose ISIS-K.

ISIS-K has largely been unable to significantly thrive in Afghanistan following the fall of the democratic government and the withdrawal of U.S. forces, but it is also no longer as fervently opposed. 

"The Taliban and the Islamic State are enemies. The Taliban goes after the Islamic State even while we're not there – that doesn't make them a counter-terrorism partner, but now they don't have the dual threat against them – the U.S. targeting the Islamic State and the Taliban targeting the Islamic State – they have greater freedom of movement," Roggio said.  

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The security expert said that when it comes to Afghanistan and the threats posed against the U.S. and its Western allies, the Taliban and al Qaeda remain a greater threat than ISIS, though he emphasized that ISIS does increasingly have "more space to operate."

"The Assad regime was an enemy of the Islamic State," Roggio said. "One of the Islamic State's enemies has been taken off the board, and therefore it will give ISIS more space to regenerate strength in an area where it already has a significant presence."

However, there is a third area where ISIS has strong roots and where it could see a resurgence should the U.S. again pull troops from the area. 

The Biden administration in September announced that, in coordination with the Iraqi government, the U.S. will end its military mission in Iraq to combat the Islamic State by 2026. The move was met with immediate concern from security experts who argued that ISIS remains a top threat to the U.S., and it could further endanger American soldiers still fighting the terrorist network in Syria. 

Specifics on the troop drawdown remain unclear, and plans to renegotiate a change to the withdrawal plans following the collapse of the Assad regime and the ambiguous state of Syria have not emerged. 

It remains further unlikely that the incoming Trump administration will push to keep U.S. soldiers in Iraq despite the threat posed by ISIS given the president-elect’s push to withdraw U.S. forces from Afghanistan during his first term. 

"The U.S. has to decide if it wants to remain in Iraq and Syria in order to counter the Islamic State and other target groups," Roggio said. "And if it decides to stay, it needs to beef up [its] presence in order to deter threats from militia groups that have been attacking U.S. troops.

"The U.S. effort to keep the Islamic State down is critical. Without the U.S. presence there, groups like the Islamic State, will thrive given the lawlessness," the security expert added. "As bad as the Assad regime was, and it was a horrible regime, it did fight the Islamic State – so without their presence, you have another terrorist organization that is in nominal control of large areas of Syria.

"As we learned in Afghanistan, you can't trust terrorists to fight other terrorists," Roggio added. 

Fox News Digital could not reach the Trump transition team for comment on his plans regarding U.S. troops in the Middle East.