The government has regained control of much of Syria with Russian backing, and a win in the south would cap a string of victories this year.
Its strategic value comes from geography: the south borders Jordan and the Israeli-occupied Golan Heights, but also lies close to Damascus.
As a result, it's a prized region for nearly all stakeholders in Syria's warped war: the regime and rebels, plus Iran, Jordan, Israel, Russia, and the United States.
Typically bitterly divided over Syria, most of those powers seem to agree on a government comeback in the southern provinces of Daraa and Quneitra.
"The southern front is the first example of international consensus for the regime's return," says Nawar Oliver of the Turkey-based Omran Institute.
The government has amassed troops in Daraa and Quneitra for weeks and dropped leaflets over Daraa city, the cradle of the 2011 revolt, demanding rebels give up.
Oliver says the south may fall without a fight.
"It's clear there's a consensus between powers -- the Americans, the Israelis, the Jordanians and the Russians -- that the better choice is for regime forces to deploy there without entering into a military operation," he tells AFP.
Rebels still hold most of Daraa and Quneitra, but pro-regime forces, including around 500 Iranian military advisers and members of Lebanese movement Hezbollah, are deployed elsewhere in the south.
- 'Sentinel' in the south -
The strange aligning-of-the-stars over southern Syria is the product of talks led by Moscow, which has leveraged military support to Syrian President Bashar al-Assad into a mediator role.
It called last week for urgent negotiations with the US and Jordan on the south, and on Thursday President Vladimir Putin discussed Syria with Israeli Prime Minister Benjamin Netanyahu.
Israel sees the south's fate in virtually existential terms, seeking to roll back its arch-nemesis Iran from Syria's border with the occupied Golan.
"International powers have reached near-consensus on the Damascus regime's return to Syria's south, with its Iranian ally distanced from the border," says Sam Heller of the International Crisis Group.
Perhaps in exchange the regime may be allowed to exert control over the neighbouring province of Daraa.
"But some parties don't trust the regime to rein in its Iranian ally and commit to distancing it from this sensitive area," says Heller.
Last month, Israel conducted unprecedented strikes on what it said were Tehran's installations in Syria, accusing Iranian fighters there of firing rockets at the Golan.
"The whole point of the Israeli zone in Quneitra is to provide sentinel on the Syrian side of the Golan Heights," says Nicholas Heras of the Center for a New American Security.
Iran, in return, would ask for "freedom of movement along the land route from Tehran to Beirut," says Oliver.
That land bridge remains a major concern for both Israel and the US, as it allows Iran to supply Hezbollah in Lebanon.
- 'Win without war' -
Russia is also seeking to appease Jordan, which hosts 660,000 Syrian refugees.
Moscow, Amman, and Washington announced a ceasefire in southern Syria last year that Heras says was a precursor to the upcoming deal.
"The dirty, not-so-secret, secret is that the US government believed from day one that the southwest Syria de-escalation zone was just an interim step toward a broader deal with Russia," says Heras.
With a regime offensive looming, Russian-led talks are Jordan's "last, best hope" to avoid a new refugee influx, he adds.
Amman could also gain from renewed trade through southern Syria if the Nassib border point is reopened.
"The Jordanians need Assad to win without war, and that is exactly what Russia is offering with the reconciliation process," Heras says.
Syrian Foreign Minister Walid Muallem hinted a deal was in the works on Saturday, but introduced yet another condition: the withdrawal of US-led forces from their eastern Syria base.
Back in Daraa, civilians watch apprehensively as world powers piece together the puzzle.
"The way the media is reporting it, the regime sent reinforcements and wants to storm Daraa, and foreign countries hold daily meetings," says Daraa resident Ahmad Abu Hazem.
"Meanwhile, people have no idea what'll happen."
Rebels, too, appear to have been left out.
"We were not consulted when the de-escalation deal was reached, and we're not looped in to current discussions," says a commander from the Southern Front, the leading local rebel coalition.
Although a full-blown assault would be catastrophic, a deal with the regime remains hard to swallow.
"Every family has someone who's been arrested or killed, since Daraa was the first to revolt," says the commander.
"Generally, civilians don't trust the regime or Russia."