Aden is a forlorn port city in the south of Yemen. It has been the capital of both a British colony and the Arabian peninsula's only socialist state. It was once the busiest port in the world. And it is probably best known today as the place where the USS Cole was bombed 15 years ago.

In October of 2014, I was lounging on dirty carpet and musty cushions spread over the dirt yard of a nondescript concrete building in the Khormaksar district of Aden. The ragtag group of young men around me, who had formed a kind of militant neighborhood watch, called the yard where we were sitting their "Operations Room."

The men claimed that they made up the backbone of Yemen's so-called Southern Resistance. "We are planning the revolution," a young man named Ali* said as we sweltered in the humid night air. "We want our country back."

One day, the men said, they would control Yemen's south, ending a 25-year-old union of two separate states that created modern Yemen. But it was hard to take them seriously. Aside from a couple of older, hard-looking men, the group of about 30 looked like a gaggle of wide-eyed overgrown boys, and they seemed no different from many others in Yemen's notoriously disorganized and chaotic southern secessionist movement.

But they were different, they insisted. They would one day lead the south to independence.

* * *

Six months later, the same young men are now running through the streets of Aden, fighting for their lives with battered Kalashnikovs they are not trained to use and for which they do not have enough bullets. They are dying in droves as they battle a far more experienced, better-supplied enemy that already controls much of Yemen's northwest and western seaboard. It is an enemy that has proven willing to indiscriminately shell the city in an attempt to bludgeon the nascent resistance movement into acquiescence.

"Almost all of them are dead, and the rest are injured," Hisham, one of Ali's companions, told me over a hissing phone line from Aden this week as fighting continued across the city. "So we have opened the door to everyone in Aden to fight. We fight a lot." He paused. "But this is our battle. This is our war. We can win."

'We could take the south tomorrow. But the next day we would run out of bullets.'

For the past two weeks, a massive campaign of air strikes by a coalition of military forces led by Saudi Arabia has been battering Yemen in the hope of dislodging a powerful Shia militia known as the Houthis from the capital city of Sanaa. But the airstrikes have had little effect, and it is becoming increasingly clear that if the tide of Yemen's rapidly evolving civil war is to be turned, it will be by young men like Hisham and Ali — if they can survive long enough.

Incredibly, Yemen's self-designated southern resistance movement has done something that battle-hardened northern tribes and military units have failed to do elsewhere in the country: halted, and maybe even reversed, the expansion of the Houthis — they are based in the north of the country — and their main backer, Yemen's former president Ali Abdullah Saleh.

Understanding who these young men are, where they come from, and what they want is essential to understanding the trajectory of Yemen's conflict, how it will affect the union that brought the modern Yemeni state into existence, and the incredibly complicated landscape the Saudis will have to negotiate if their first military adventure in decades is to be a success.

* * *

The resistance movement in Aden is fighting against an uneasy alliance made up of two main groups. One is comprised of military units loyal to Saleh. The other are fighters from the Houthis, a onetime Zaydi Shia revivalist movement based in Yemen's northern highlands that has been in control of Sanaa since last September. The Saleh-Houthi alliance started moving into the south of Yemen last month after the country's deeply marginalized president Abd Rabbu Mansour Hadi, who had earlier fled to Aden after a month under house arrest in the capital, announced plans to form a 20,000-man militia to oust the Houthis with backing from Saudi Arabia. Faced with the rapid advance of alliance forces, Hadi took flight again, this time to Riyadh. With their man in Sanaa having fled Yemen and the Houthis primed to consolidate their control over the country, the Saudis — who view the Houthi Shia militia as a proxy for their longtime enemy, Iran — decided that enough was enough.

With the backing of 10 other Sunni states, the Saudis launched a huge aerial campaign in Yemen aimed at decimating the Houthi-Saleh alliance's military capabilities. They have said they will not stop until the Houthis surrender more or less unconditionally and Hadi is restored to the presidency. But Saleh and the Houthis have only intensified their efforts to take Aden, where they have met far sterner resistance than they had expected. And so instead of Saudi airstrikes, it is an inexperienced and under-resourced group of irregular southern fighters that is causing the alliance headaches. No one is more surprised by this than the southerners themselves.

It makes sense that the Saudis and Hadi (himself a southerner) see the resistance movement in Aden and elsewhere in the south as natural allies in their fight against the Houthis. In fact, the Saudi-led coalition has gone so far as to claim that the forces fighting the Houthis and Saleh in the south of Yemen are part of their coalition, often describing them as "pro-Hadi" militias. Brigadier General Ahmed Asiri, the spokesman for the Saudi-led campaign, has said that the campaign's backers are in the process of "working in Aden to make it safe."

This version of events fits into a popular narrative of a war in Yemen made up of two neat coalitions: on one side the Houthis, an Iranian proxy backed by Saleh, who hopes he can use the current conflict to restore his family to power. On the other, Sunni Yemenis from the north and south rallying around Hadi who are backed by Saudi Arabia and the Gulf states and intent on restoring Hadi to the presidency. It's a story that helps make a complex country easier to understand.

The problem for the Saudis is that many of those doing the fighting in the south have long shared a single goal — one that Hadi has said, explicitly and repeatedly, he does not endorse: independence from the north.

When I ask Hisham what he thinks of Hadi, he laughs.

"Why do we have to support Hadi?" he asks. "There are no Hadi people here. The people fighting are Adenis. We are receiving nothing at all…. He is not supporting us."

* * *

In early 1990, there were two Yemens: the northern, republican Yemen Arab Republic and the southern socialist People's Democratic Republic of Yemen. Both countries struggled in the wake of the Cold War, when what had been plentiful patronage from the West and the Soviets was suddenly cut off. That year the two countries' presidents, the northern republican Ali Abdullah Saleh and the southern socialist leader Ali Salem al-Beidh, hastily agreed to enter into a unity deal based on a loose power-sharing agreement apparently aimed at sharing resources to keep the now-unified state afloat.

But officials from the south working in Sanaa, the capital of the unified state, soon began to complain that they were being marginalized by the clique of tribal, military, and Islamist forces that Saleh had used to rule the north for the previous decade and a half. Saleh, they worried, was more interested in exploiting the south's oil and gas riches than he was in working with southerners to build a new country.

In 1994, al-Beidh tried to unravel the deal, returning to Aden and declaring southern independence. But the northern military, bolstered by tribal militias and jihadists recently returned from the war in Afghanistan, made short work of the secessionists. Within three months they had routed the remnants of the southern military and had consolidated their control over Aden. The spoils of war, including land, businesses, and oil fields, were divvied up among the different factions of the Saleh regime. Southerners complained incessantly over the next two decades of political and economic marginalization, gradually forming a protest movement known in Yemen as Al Hirak al Janoubi [the Southern Movement] — or, more commonly, Hirak.

Hirak distinguished itself by remaining largely peaceful, although this was in no small part due to the inability of its many factions, ostensibly led by former dignitaries mostly living in comfortable exile, to form a united front. The movement made little progress. Most of the major Hirak groups refused to take part in peace talks in Sanaa in 2013 and 2014, held after the country was almost torn apart by a schism within the Saleh regime that led to fighting on the streets of Sanaa.

'These old men are nothing to us now. All they did before is talk. They are not here and they are not fighting. We will get our country back.'

The southerners also became rapidly disillusioned with Hadi, a southerner brought in to replace Saleh as an ostensibly unifying force. His popularity was hardly boosted by his decision to bring in a group of southern exiles and unknowns to take part in the Sanaa peace talks in 2013 who were widely wide seen as ringers brought in to represent the new president's personal interests. One of the few recognizable southern leaders Hadi invited, a man named Mohammed Ali Ahmed, quit the talks soon after they began, claiming that the president was simply asking him to rubber-stamp decisions no southerner would ever accept.

"Hadi has no authority," Abdulkader Suleiman, one of the older men in the group I sat with in Aden last year, said when asked what he thought of the president. Suleiman was from Abyan, Hadi's home province. Abyan borders Aden to the east and has long been seen as a hotbed for the local al Qaeda franchise. Suleiman joined the irregular militias, the Popular Committees, to help push al Qaeda out of Abyan in 2012. Like many who fought there, he became disenchanted with the campaign, which he said was largely for show. He was angered by the number of his men who died in the fighting, and by Hadi's decision to cut payments to the fighters while continuing to claim their fealty in public. Hadi was little more than a northern puppet, Suleiman said.

By 2014 southerners had also lost patience with the bluster of exiled southern leaders in their 60s and 70s who harkened back to the days of the British or the socialists but did little to effect separation from the north. So they formed their own grassroots movements — like the one I visited in Aden — aimed at getting independence on their own terms. There was, however,one big problem: a lack of resources.

"We could take the south tomorrow," Hisham confided to me during a drive around the city the same night we sat in the Operations Room. "But the next day we would run out of bullets."

That explains the backing Hadi enjoyed in the south after fleeing Sanaa, which was predicated on the perception that he could act as a conduit for Saudi cash, says Fernando Carvajal, an American academic and NGO consultant who enjoys a close relationship with many southern groups. Support for the ousted president lasted as long as his checkbook was open.

"No one group in Aden has publicly expressed direct support for Hadi as president, and his statements during his only televised speech [in which he reaffirmed his support for unity] before departing to Saudi proved to the people Hadi will not work toward secession," Carvajal says. "This limits the support he can publicly receive from anyone in Aden."

In the rest of the south, he adds, Hadi has "no support in any form."

This makes life difficult for the Saudis, who have built their campaign in Yemen around Hadi's legitimacy as leader. The ousted president personally asked for the military intervention, which could soon see Saudi and Egyptian boots on the ground. That's probably why there is such a glaring disconnect between what people in Riyadh are saying — that the resistance in the south is backing and backed by Hadi — and the reality on the ground. No one wants to launch a war aimed at restoring a leader who isn't wanted back by even the people who should be his natural allies.

Hadi and other southerners may also be doing their best to mislead the Saudis on the matter. Sources in Riyadh tell VICE News that Hadi, his few remaining supporters, and some of south Yemen's better-known former leaders have converged on the Saudi capital, telling officials there that they are in contact with the resistance movement, and that they are in the process of putting together a coalition of forces to take the fight to the Houthis. These people, who include families of the sultans who ruled under the British and former socialist leaders, have reportedly said that if the fight can be won with Saudi backing, they will not immediately raise the issue of separation, instead opting for a system of federalism for five years before a referendum can be held on independence, much like what happened in Sudan.

I suggest to Mohammed, another young man fighting in Aden, that such a deal is being put on the table.

"These old men are nothing to us now," he says, clearly angry. "All they did before is talk. They are not here and they are not fighting. We will get our country back, God willing."

* * *

The Saudis know that taking a position on unity will endanger their ability to build support in the south, Carvajal says. '[T]he royals leading military operations have not expressed any support for secession, leaving one to assume [Saudi Arabia] remains committed to Yemen's territorial integrity as one state — and with Sanaa as its capital, not Aden."

The Saudis will need support from northern tribes if they are to break the Houthis-Saleh alliance's grip on the north, making their position in the south even more perilous. Several members of Islah, the northern Sunni party, tell me that their handlers in Riyadh are encouraging them to send their people south to help push the Houthi-Saleh alliance back before launching an offensive on Sanaa. Islah has publicly backed the Saudi campaign and has called for the liberation of the south from the Houthi-Saleh alliance.

But southerners recall the role that Islah played in brutally putting down the 1994 secession attempt and subsequently looting southern land and resources. While southerners are happy to accept financial support and arms from the Saudis, they have no interest in inviting northerners to come, armed, into the south. And anti-northerner rhetoric has reached new heights since the Houthi-Saleh alliance started indiscriminately shelling homes in Aden in an effort to crush the resistance. Many southerners say that the Houthis, Saleh, the northern tribes, and Islah are all cut from the same cloth and are not to be trusted.

If Saudi Arabia or Egypt were to send troops into the south to help secure the area, Hisham says, "we will be together." But if tribesmen or Islamists from the north enter the south, it will be a different story.

"They want to make the united Yemen strong," he says. "Unity is over. If they are coming, we will fight them."

_Follow Peter Salisbury on Twitter: _@altoflacoblanco