Peter Bergen is CNN's national security analyst, a vice president at New America, a professor of practice at Arizona State University and chairman of the Global Special Operations Foundation. He is the author of " United States of Jihad: Investigating America's Homegrown Terrorists ."

(CNN) The battle in Niger in which four members of a US Army Special Forces team were killed by an ISIS-affiliated group has garnered a great deal of public attention, partly because of the spat between President Trump and the family of one of the dead soldiers, Sgt. La David Johnson, but the incident also underlines the extent to which the war on terror has truly globalized since the 9/11 attacks.

A US National Counter Terrorism Center map from 2016 shows 18 countries with official branches of ISIS and an additional six countries where there are "aspiring branches" of the terror group.

One of those official branches of ISIS is an offshoot of the notorious Nigerian terrorist group, Boko Haram, which operates not only in Nigeria but also in neighboring Niger, the country where the four US Army soldiers -- two of them Green Berets -- were killed on October 4.

It's the increasingly globalized nature of ISIS and like-minded groups that is a key reason for the large number of countries around the globe where US Special Operations Forces are now deployed.

According to a Pentagon press release from July, about 8,000 Special Operations Forces are deployed in 80 countries around the world.

There are around 800 American soldiers now stationed in Niger , a number of whom are US Special Operations Forces, although their precise number isn't clear.

President Obama -- elected, in part, on his promise to end large scale wars in the Muslim world -- increasingly turned to using Special Operations Forces and drones as a way to combat terrorist groups.

President Trump has continued this policy.

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The classic role of Special Forces, including the Green Berets that are now deployed in Niger, is to work "by, with and through" local forces.

In practice, this means advising local military and paramilitary forces so that small teams of Green Berets working on the ground can act as force multipliers for the much larger units they are advising.

The classic example of how successful this approach can be was the overthrow of the Taliban in Afghanistan in the winter of 2001, which was accomplished by some 100 US Green Berets on the ground calling in American airstrikes. The Green Berets also allied with many thousands of Afghan militiamen to defeat the Taliban.

The Obama and Trump administrations' reliance on Special Operation Forces and drones in many ways is a sound policy. There is no desire from the American public for large-scale ground wars against groups such as ISIS and al Qaeda. Not only are these costly in blood and treasure, but such large-scale interventions are often not necessary to fight relatively small terrorist groups.

Take the fight against the hundreds of militants affiliated with ISIS who in May seized the city of Marawi in the southern Philippines. US Special Operation Forces provided assistance to the Filipino military forces that seized back control of the city this past week.

Similarly, in Syria, 300 US Special Operations Forces advised the Syrian Democratic Forces, which took control of Raqqa, ISIS' de facto Syrian capital, earlier this month.

For all the advantages that special operations have in their light footprint and flexibility, there can also be a significant disadvantage as perhaps applied in the Niger case -- that it may be harder for US forces to come to the aid of those in a firefight. While a full accounting of what happened in Niger may take many weeks, those are the kinds of questions the firefight raises.

The largely covert war fought by Special Operations Forces in countries around the world relies on the Authorization for the Use of Military Force (AUMF) that Congress passed just days after 9/11 authorizing President George W. Bush to "use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, or harbored such organizations or persons...."

Today, two presidents later, this is the same authorization that is invoked to enable Special Operations Forces to conduct military operations in West Africa, North Africa, the Middle East, South Asia, and Southeast Asia. Obviously, few of these operations have anything to do with the 9/11 attacks.

No one imagined that the post-9/11 AUMF would 16 years later be the legal authorization for numerous military operations against jihadist terrorist groups across the globe.

It would be wonderful if Congress would have a public debate about the scope of these operations, rather than handing the president effectively a blank check, but few in Congress have been willing to bring the matter to a vote and so America's long wars grind on with little public discussion or congressional debate.

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Even some well-informed senators were surprised when -- following the attacks on the US Special Forces team in Niger -- they found out that hundreds of American soldiers are stationed there. (Congress, in fact, had been notified of the Niger deployment, but the notification was routine and garnered scant attention.)

The likelihood that Congress will assume its proper responsibility to have a vote on a new authorization for the use of military force is quite low. Few in Congress have forgotten the cost that Hillary Clinton's 2003 vote in favor of the Iraq War had for her presidential ambitions when it came to the primary challenge mounted against her by Barack Obama.