President Trump’s inexplicable fight with the widow of a Green Beret who was killed in Niger has sparked a political firestorm that shows no signs of dying down. It’s also brought new attention to a little-known aspect of Washington’s ongoing war on terror: The Pentagon is rapidly expanding its presence in Africa and is now engaged in military operations — including active combat — in more than half a dozen African countries.

It’s a fight that takes place largely in the shadows, led by small teams of US special operations forces. In Somalia, Navy SEALs are hunting members of al-Qaeda and ISIS-linked militants from groups like al-Shabaab (one of the commandos died in a botched raid earlier this year). In Libya, they’re carrying out counterterror missions like the one that captured Ahmed Abu Khattala, a militant linked to the deadly assault on the American diplomatic compound in Benghazi. And in Djibouti, the US flies armed drones out of a major airbase at Camp Lemonnier, which is also used for counterterrorism and counter-piracy operations in the region.

US forces have also regularly conducted raids and other missions in Chad, Cameroon, Uganda, and, of course, Niger, where there are at least 800 American troops deployed.

The missions rely on a broad array of legal authorities but have one particularly important thing in common: They have never been specifically authorized by Congress, let alone discussed and debated by the American public. Huge questions exist as to the strategic importance and relevance of all these missions, and whether they improve US national security enough to justify the high cost in blood and treasure. Since 2001, at least 36 soldiers have died conducting or supporting military operations in Africa, including Sgt. La David Johnson and the three others killed in Niger earlier this month.

With 6,000 troops operating in Africa, and US commanders describing the continent as the next big battleground in the terror fight, the pace and number of American military engagements is certain to increase even more sharply. That raises legitimate new questions about whether the US has committed itself to unending and expanding war in Africa through missions that are taking place with nearly no political or public oversight.

Niger is getting the headlines, but it’s a small part of what the Pentagon is doing in Africa

As Zack Beauchamp has written for Vox, the US has been working with governments in heavily Muslim West Africa to counter local Islamist groups since the George W. Bush administration. The US presence there ramped up considerably under the Obama administration, which sent special forces to train and assist local partners in countering both al-Qaeda and ISIS groups.

None of these missions have been specifically debated, much less authorized by Congress; Sen. John McCain has already talked about issuing subpoenas to the Pentagon for more details about the mission in Niger. For operations against al-Qaeda-linked groups, the Pentagon relies on the old post-9/11 Authorization for the Use of Military Force as its legal authority. In the aftermath of the botched mission, there’s a new push in Congress to repeal that legislation and require the Trump administration to seek a new one, but it’s not clear if those efforts will pay off. In the meantime, the military continues to operate in the shadows across Africa.

Most US missions aren’t intended to involve any form of combat. Instead, they’re designed to help African nations build up their own capacity to fight militants inside their borders without American help. The theory underlying all of these missions is that it’s cheaper, less risky, and more effective to train and equip local forces to fight than rely on American troops operating far from home on unfamiliar terrain. The problem is that it’s not clear those types of missions work — let alone serve broader US security interests.

The US is fighting in multiple African countries with nearly no political or public oversight

However, in countries like Niger and Mali, the US has struggled to build effective local capacity to fight terrorism, in part because of the difficulty of the task and the relatively meager resources allocated (tens of millions of dollars, compared to the billions spent in places like Afghanistan or Syria).

In her forthcoming book, former Pentagon official Mara Karlin concludes that “in practice, American efforts to build up local security forces are an oversold halfway measure that is rarely cheap and often falls short of the desired outcome.” Kings College London professor Walter Ladwig pins many of these failures on rifts that emerge between the patron (like the US) and the client in these relationships. Ladwig studied three major cases of military aid — Vietnam, El Salvador, and the Philippines — and found that the US did well managing the relationship in just one of these (the Philippines), while doing a fair job in El Salvador and a disastrous job in Vietnam.

Others, like Naval War College professor Jonathan Caverley and Trinity College Dublin professor Jesse Dillon Savage, have noted that security assistance can have a destabilizing effect by effectively forcing Washington to choose sides in local conflicts and empowering the military at the expense of civilian politicians. In 2010, a military junta overthrew Niger’s president; democratic elections were held in 2011, and another military coup attempted to overthrow that president in 2011.

As Nick Turse noted for the Intercept, Chad’s military launched coup attempts in 2006 and 2013, the Mauritanian military toppled the civilian government in 2005 and again in 2008, and a US-trained military officer ousted the democratically elected president of Mali in 2012. The latter coup helped set the stage for an al-Qaeda affiliate to conquer a broad swath of the country before being pushed out by a French-led military coalition.

The bottom line is that it’s impossible to predict when, or if, training local militaries will help US interests or regional stability. Over the past 75 years, the US has successfully helped local forces win, as in 1947 with Greek forces fighting the communists, in the 1980s helping Afghan fighters defeat the Soviets, in 1995 helping Croat forces battle the Serbs, or more recently in Iraq, helping local units retake Mosul. The problem is that the list of failures is even longer — and that success doesn’t always further US interests in the long run, as seen most clearly in Afghanistan.

A second major risk is that these operations can quickly escalate from training or advisory efforts into combat operations — often when least expected, and at the initiative of the enemy. That appears to be what happened in Niger.

Johnson and his fellow soldiers were advising Nigerien military on the ground, seeking to improve their ability to fight al-Qaeda- and ISIS-linked fighters leaking over the porous border with Mali. On October 4, an Army Special Forces team (composed of 12 soldiers) set out on a patrol with its Nigerien counterparts along the Niger-Mali border. Intelligence told the team they faced little chance of enemy contact on this reconnaissance mission. Although US military forces had conducted nearly 30 similar missions in that area before, October 4 was only this particular team’s second such mission in Niger.

NBC News reports that the mission changed at some point from reconnaissance to something more like a “kill/capture” mission, focused on insurgent leader Adnan Abu Walid al-Sahraoui. The joint US-Nigerien unit was ambushed on October 4, suffering heavy casualties.

The Pentagon is hunting terrorists across Africa. Sometimes the terrorists strike first.

The Pentagon wants to keep its troops out of harm’s way. That may not be possible.

Modern US advisory efforts attempt to minimize risk to American forces like those killed in Niger by distinguishing between “train and assist” and “advise, assist, and accompany” missions. In the former, US troops generally stay on well-secured bases or embassy grounds, providing training or remote assistance where allowed by their mission parameters. In the latter, US troops actually accompany local forces on their missions, exposing themselves to the same risks as their counterparts battling al-Qaeda or other violent extremists.

The latter type of mission — the kind where US forces face risk — is far more effective. However, it exposes US troops, often in places where the US has no military infrastructure for combat air support or medical evacuation.

This is the third risk unique to these small (“light footprint” in Pentagon parlance) operations: They expose troops to tremendous risk by their very nature. Special forces teams, like the one ambushed on October 4 in Niger, are incredibly skilled but carry minimal weaponry and cannot fight their way out of battles with numerically superior foes, nor survive when they sustain large numbers of casualties. These advisory missions frequently rely on local health care facilities or allied forces for medical evacuation and treatment, or rely on nearby embassies or intelligence personnel to obtain such support, because they rarely deploy with their own organic evacuation helicopters and medical units.

Consequently, when troops on these advisory missions do find themselves in combat — as they often do — they may be more vulnerable than conventional troops to taking large numbers of casualties, or even having comrades captured or left missing, as appears to have happened with Johnson in Niger.

In a Monday press conference, Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, repeatedly highlighted the risks inherent in this kind of mission, especially when acknowledging that it took the military two full days to find Johnson’s body. “This is a very complex situation that they found themselves in, a pretty tough firefight,” Dunford said, going on to add that Pentagon leaders still don’t quite know whether the mission switched from reconnaissance to something else, and, if so, on whose orders.

"I don't know how this attack unfolded,” Dunford said bluntly.

What’s clear, though, is that a larger, more robust force — like the kind the US has mostly fought with in Iraq or Afghanistan, or deployed to combat Ebola in Africa — would likely have more support on standby, and more ability to respond to an ambush than the small Special Forces team that made contact in this instance.

In this case, the Special Forces teams in Niger had conducted similar missions in this location on 29 occasions prior to the October 4 ambush. (That pattern itself may have played a role in the incident, by showing enemy forces there was a target to be attacked, and inducing a kind of complacency among the US Special Forces troops themselves about the risks on these patrols.) Washington has reportedly been operating in the country since 2002, with American personnel working with Nigerien forces on the Mali border and leaked Pentagon documents suggesting the construction of a major US airbase in central Niger for the operation of drones and other American aircraft.

Can the US prevent a major war by launching a bunch of smaller ones? Africa may provide the answer.

Unfortunately, the trigger for whether a given mission like the one in Niger ends in combat isn’t in American hands. Just as enemy forces in Iraq and Afghanistan frequently decided when and where combat would erupt, so too did extremist elements in Niger. And so it is with all these “light footprint,” advisory missions: The enemy gets a vote, and often the deciding vote, as to when and where these missions will go from training to fighting.

This fact highlights the fourth and broadest risk of these operations: They share a tenuous link to US national security, and leave many questions about what, if anything, is purchased with them for our benefit (as opposed to be benefit of the local forces we arm and train). In theory, security assistance missions go to countries that are fighting a common enemy, such as Afghanistan or Niger. These missions represent an “economy of force” approach to warfare: easier, cheaper and more efficient to send a few advisers to build up local forces, and have them fight, than to fight these wars with thousands of US troops.

These missions also reflect a growing belief among national security professionals in the importance of preventive war — something that also goes by other names, such as gray zone operations, shaping operations, or “Phase Zero” operations. Just as it is more efficient to fight wars with proxies, so too is it more efficient (and effective) to prevent larger wars by fighting small ones wherever possible.

This theory currently justifies an expansive view of military activity from naval patrols in contested waters to advisory missions in Southeast Asia to the assorted advisory missions in Africa. The Joint Chiefs of Staff and other senior military leaders have adopted this approach as part of official US military doctrine, embracing the view that persistent conflict at a low level is the best way to prevent large-scale wars from breaking out.

The theory has worked in some places. US advisers in Colombia did, eventually, help the Colombian government achieve a stunning victory over the rebels and narcotraffickers there. US military units have successfully trained with local forces in Southeast Asia for many years, boosting the effectiveness of military forces they work with. American efforts to support African military units operating as part of AMISOM against Somali militants have also worked well, aided by targeted strikes conducted directly by US special operations forces. Most of these missions have unfolded in the background — not deliberately hidden as covert, but not trumpeted either.

That lack of public attention has often been a good thing, enabling US military units to sustain efforts over a period of years and enabling local forces (and their political leaders) to work with US forces when that might not always be a popular thing.

However, the great downside has been a massive expansion of US military operations without any meaningful political oversight, let alone a specific vote, like the war in Iraq. “The war is morphing,” Graham said after a briefing from Defense Secretary James Mattis on military operations in Africa. “You’re going to see more actions in Africa, not less; you’re going to see more aggression by the United States toward our enemies, not less; you’re going to have decisions being made not in the White House but out in the field.”

McCain, the powerful chair of the Senate Armed Services Committee, admitted as much when he called for a congressional debate over whether continued US military operations in Niger were lawful and necessary. However, past congressional efforts to review and possibly revise the post-9/11 authorization for the use of military force have failed, and there is no reason to think a Niger-focused debate will be any more successful.

And that means that Johnson and Staff Sgts. Bryan Black, Jeremiah Johnson, and Dustin Wright are the most recent US soldiers to fall in Africa, but they won’t be the last.

Phillip Carter and Andrew Swick are both former Army officers and veterans of Iraq and Afghanistan, respectively, who are researchers at the Center for a New American Security in Washington, DC.