For a newcomer to Aden, the city’s many checkpoints are little more than a blur of black, blue, red, and white flags planted in the rubble, surrounded by young men casually toting worn semiautomatic rifles.

But for residents of the Yemeni city — a crumbling, humid port on the southern tip of the Arabian Peninsula — the checkpoints are markers of invisible borders separating the many armed groups controlling different parts of Aden. And straying into foreign territory can have fatal consequences.

“We cannot go to the port,” a Salafist fighter in the central Mansoura district says of another district controlled by secessionist militias. “There would be a big fight.”

Aden is a microcosm of Yemen’s complex and constantly shifting political geography. Deals are made and just as quickly break down, eroded by lack of trust, tribal bickering, or money — which is sometimes paid by hard-line jihadists. Gun battles could be heard throughout the city as we filmed the first episode of the new VICE News show Terror, focusing on the fight against al-Qaeda in the Arabian Peninsula (AQAP).

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U.S. special operations forces arrived in Yemen in April, aligning with the United Arab Emirates in supporting a faction of fighters from Yemen’s south. The focus for the U.S. is the eradication of AQAP, but lending their support to the fight could come with unintended consequences, among them a renewed push by Yemeni secessionists and potentially explosive infighting between forces backed by key American allies in the region.

“ISIS is here, al-Qaeda is here. They walk freely on the streets; sometimes they set up checkpoints,” our nervous driver told us as we cruised over a bridge toward Bureiqah, a strip of land west of the city that’s currently home to Salafist fighters, AQAP fighters, and Islamic State militants.

In Aden, the driver said, “You never know who might be up ahead.”

Yemen is the home of AQAP, a resilient and especially violent branch of al-Qaeda that was responsible for a series of attempted airplane bombings in the late 2000s and early 2010s. It also claimed responsibility for the 2015 Charlie Hebdo attack in Paris.

Last April, in an attempt to strike back against AQAP, the U.S. sent special operations forces to assist elite United Arab Emirates troops on the ground in the south of Yemen. At the time, the White House said it was a temporary mission. “We view this as short-term,” Captain Jeff Davis, a Pentagon spokesperson, said in May. But by July the Pentagon was quietly announcing that the mission would be extended — indefinitely.

The U.S. doesn’t have a great track record when it comes to picking friends in Yemen. Washington’s ostensible partner in the fight against extremists there was once President Ali Abdullah Saleh, a wily autocrat who, when faced with an uprising during the 2011 Arab Spring, sent U.S.-trained and -equipped security forces to crack down on protesters and engage in open warfare with his political rivals on the streets of the capital Sana’a. Still, the U.S. hesitated to call for Saleh to back down.

“If Saleh goes, the two likeliest outcomes are anarchy or a government that is not as friendly,” an unnamed U.S. official told The New Yorker’s Dexter Filkins at the time. Saleh did eventually step aside, and his longtime vice president, Abd Rabbu Mansour Hadi, took over. If anything, Hadi was even friendlier to the U.S. — but the outcome was, indeed, anarchy.

Yemen’s current civil war was sparked by a 2014 coup against the Hadi government by the Houthis, a Shia group from the north of the country who stormed and seized the capital, taking over the main government ministries. In March of 2015, Saudi Arabia, fearing the rise of Iranian influence in the region — the Saudis see the Houthis as a proxy for Iranian interests — entered the fray. Hadi fled to Saudi Arabia, where he remains; the Saudis launched a blistering campaign of aerial bombardment and announced the formation of a military coalition to retake the country.

The bombardment continues, enduring ongoing criticism for what NGOs and aid groups say is a disregard for civilian deaths that equates to indiscriminate warfare. The air war is being waged with American support.

Greg Archetto spent 10 years working for the State Department and the Department of Defense, overseeing U.S. military support for the government of Yemen in the early 2010s before leaving government in 2015 due to what he says are America’s shortsighted counterterrorism policies. He contends U.S. officials were often baffled by the constantly shifting patchwork of alliances and rivalries on the ground in Yemen; even Saleh’s regime, he says, often used the threat of AQAP to secure money and military training from the U.S. that Saleh then used to battle not al-Qaeda, but his rivals, the Houthis.

“I don’t know how you put lipstick on this pig,” Archetto said of the fighting in Yemen. “It’s tribal intrigue. One day people are on your side, and the next they have shifted allegiances.”

Early on in the civil war, AQAP seized Mukalla, a port city to the east of Aden, where, through local proxies, it ran the port, earning an estimated $2 million a day and building what Reuters estimated was a $200 million war chest. When VICE News was in Aden earlier this year, AQAP personnel walked the streets openly and hosted meetings in the Mansoura district, where the local AQAP emir lived in a compound well-known to locals.

Aydrous Zubaidi is the commander of the militias, brought in to Aden from the north to restore order in December 2015, when he was named governor. Within two months, he had already survived at least three assassination attempts.

“The main challenge is terrorism,” he told us in his fifth-floor office at the main government building in Aden. “The infrastructure of the city was destroyed…. [Al-Qaeda] became prominent while people weren’t paying attention during the war.”

Since our visit to Aden, Zubaidi’s men, backed by the UAE, were able to push AQAP out of the city. But their success edged the country closer to a different kind of destabilization: It gave hope to many southern Yemenis who have long wanted to secede from the rest of the country and reinstate the north-south border that divided Yemen until its unification in 1990.

The south last attempted to secede in 1994, but the movement was crushed by a Saleh-led coalition that included jihadist returnees from Afghanistan, some of them linked to the then little-known Osama bin Laden. A new secession attempt would be a problem for the U.S., which doesn’t want yet another civil war in Yemen further undermining its efforts to destroy AQAP. It would also be a problem for Saudi Arabia, which says it entered the fray in Yemen to keep the country together, not to see it split in two.

Many southern separatists see the UAE as their most likely foreign ally. The Emiratis were the principal architects of the campaign against the Houthis in 2015, sending U.S.-trained Emirati Special Forces troops, who had operated on the ground in Afghanistan alongside Americans, into Aden during the early months of the war to help coordinate the multitude of local militias.

A European diplomat who works on Yemen and would only speak anonymously because he was not authorized to do so told VICE News that the Emiratis “take point” in the south while the Saudis focus on the north.

Leaders of both Sunni countries want to send a signal to Shia Iran, but the UAE has a well-documented antipathy toward political Islamists, particularly the Muslim Brotherhood. Many of the groups fighting the Houthis in the north of Yemen are affiliates of Islah, Yemen’s main Sunni Islamist party, which the Emiratis see as a wing of the Brotherhood. In 2014, the UAE named Islah a terrorist organization.

As the war has dragged on, the Emiratis have quietly begun to develop a contingency plan for southern independence, three people briefed on the matter told VICE News. But the Saudis won’t currently accept the idea of an independent southern Yemen. Peace talks over a negotiated end to the conflict raging in central and northern Yemen took place in Kuwait between April and August, but no agreement was reached.

If a peace deal is agreed to but the issue of southern secession is not addressed — it was not on the agenda in Kuwait — the end of the civil war in the north could lead into yet another civil war over secession that envelops the entire country, pitting forces backed by two regional U.S. allies against each other.

It is into this powder keg that the U.S. has inserted itself with the stated aim of defeating AQAP, seeking to do so by indirectly backing yet another faction: a UAE-trained fighting force made up entirely of men from Hadramawt, a province in southeastern Yemen. In April, Hadrami militias entered Mukalla, the port town in southern Hadramawt controlled by AQAP, and pushed the militants out. U.S. special operations forces were sent in to advise UAE forces on the ground on how to continue the campaign against AQAP.

Many Hadrami militias would like to see Hadramawt become an independent state or autonomous region rather than part of a broader southern Yemeni state — a secession within a secession. Since taking Mukalla, the militias have begun a campaign of arrests, breaking into the homes of Islamists, abducting them, and sending them to a detention center at an unknown location, multiple sources inside Mukalla said. Many of those arrested are members of Islah — the group the Saudis are backing in the north and the UAE considers terrorists.

“When the threat of the Houthis subsides, it’s far from out of the question that the different groups who have been fighting them turn their weapons on each other,” said Adam Baron, a Yemen expert and a visiting fellow at the European Council for Foreign Relations.

Several U.S. defense officials who spoke to VICE News said that the U.S. special ops contingent in Yemen is small and does not work directly with the Yemenis, nor are there plans to scale up. America’s sole partner on the ground is the UAE.

“We have some very specific goals in Yemen,” a former Defense Department official with knowledge of the deployment said. “Degrade and disrupt AQAP and IS. There is no constituency objecting to that right now.”

U.S. personnel were deployed in part because of preexisting relationships between members of the U.S. special operations team and UAE special forces who had also served in Afghanistan. In fact, the biggest push for the U.S. team to enter Yemen came from the leadership of the team itself, two people with knowledge of the mission said.

“I don’t think either the U.S. government or maybe even the Emiratis have a really great fidelity on who they are working with beyond the main leaders on the ground, and where their allegiances lie outside of a very immediate tactical goal,” said the former Defense Department official. In other words, the Americans and their regional partners know who they work with directly — but not necessarily who those people are working with.

According to an advisor to the U.S. government on Yemen, the U.S. has not considered the longer-term implications of indirectly supporting southern separatists, and has not done any contingency planning for a move by the south to secede.

VICE News contacted the National Security Council, which oversees high-level security planning for President Barack Obama, to ask about strategy on Yemen. The council referred us to the Defense Department. A spokesperson there declined to answer questions about the makeup of the U.S. forces operating in Yemen, and referred us to the United States Central Command, which oversees U.S. military interests in the region.

They have yet to respond to a request for comment.

“The [special operations forces] do their jobs well,” Archetto said. “They completed their task from an operational standpoint.” The problem, he said, is that higher-ups weren’t vetting the people the U.S. was training and arming. And he fears that could lead to a situation not unfamiliar to the U.S.: