CAIRO -- As Saudi Arabia tightens the screws on its weak southern neighbor, the war it launched in Yemen over two years ago appears more intractable than ever, with nothing but further suffering in sight.
Despite crushing air power by the Saudi-led coalition seeking to reinstall the country's exiled president, which has reduced much of the north to rubble, Yemen's Shiite rebels, with the political backing of Iran, still hold large swaths of territory, including the capital, Sanaa.
And while the U.S.-supported coalition's recent tightening of a blockade to include aid shipments might be intended to starve the rebels into submission, they remain dug in to difficult, mountainous and urban terrain.
Unlike other regional conflicts in Syria or Libya, no side is winning, and peace talks are nonexistent. With both sides deeply committed to victory, face-saving exits are elusive, especially with the Saudi-Iranian rivalry heating up. The war, which has killed more than 10,000 civilians and pushed millions of Yemenis to the brink of famine, appears unlikely to end any time soon.
A look at the impasse:
HOUTHIS WEAKENED BUT DUG IN
On much of the ground and especially in the north, the battle-hardened Shiite rebels known as Houthis hold the upper hand. They control most state institutions and fortifications, are well-armed, and are backed by the remnants of a powerful army built up by former President Ali Abdullah Saleh. Infrastructure, such as health care, water and electricity however, are failing.
Opposing them are a jumble of forces ostensibly loyal to exiled President Abed Rabbo Mansour Hadi, and a collection of tribes under nominal tutelage of Saudi Arabia and its main coalition partner, the United Arab Emirates.
These forces control most of the south, including the port city of Aden, Yemen's second largest and the official seat of Hadi's government, but a place where weak security, local factional power struggles and repeated attacks have kept him away for most of the year.
Neither the Saudis nor the UAE appear to have forces capable of taking over the whole country. An earlier drive northward ended up in tragedy for the coalition, with over 100 Emirati soldiers killed in combat so far.
NO LEADERS LEFT
After all the fighting, to say Yemen lacks leaders with broad consensus is an understatement.
The Houthis, a long-neglected Shiite offshoot in the north, consider themselves revolutionaries fighting corruption. But their enigmatic leader, Abdul-Malik al-Houthi, appears only rarely, and his appeal has little reach beyond the bounds of sectarianism.
Likewise, his erstwhile ally Saleh, who once mastered the country with a deft tribal balancing act until he was deposed in a 2011 Arab Spring uprising, now has little comprehensive appeal, although some yearn for the pre-war days when he ruled. The two have reportedly fallen out, with news occasionally surfacing that the Houthis have put Saleh under house arrest.
Hadi, meanwhile, has fared no better as a potential leader of a post-war Yemen. Now in exile in Riyadh, the Saudis have prevented him from travelling to Aden since February, saying it's not safe. As his influence waned, the UAE built up its own force in the area, training and financing militias loyal to it.
THE COALITION'S COMPETING AGENDAS
The UAE's rising clout in the south, where it has backed alternate local leaders, has led to friction with Hadi and further undermined his rule.
And while not at odds with the Saudis, the UAE prefers supporting ultraconservative Salafi groups as a bulwark against Islamist organizations it loathes, like the local branch of the Muslim Brotherhood, which the Saudis have given a pass in Yemen.
Riyadh has also historically been more tolerant of more hard-core Sunni-inspired fighters, blurring the lines regarding who the coalition should consider friend or foe in southern Yemen. Al-Qaida and Islamic State group affiliates operate there, sometimes striking targets in Aden and other southern cities.
The same goes for the lawless east, a vast desert with little state control and occasional U.S. drone strikes on militants. While minor, the differences highlight potential pitfalls in efforts to unify the south, let alone the larger country with its diverse tribal mosaic.
While the Saudi-led coalition's air power and naval blockade cannot bring victory on its own, it has made a large-scale Iranian intervention nearly impossible.
Tehran, while ideologically close to the Houthis and happy to give them political and diplomatic backing, denies supplying them with weapons. Small arms shipments on fishing boats are occasionally intercepted en route to Yemen, and both the U.S. Navy and coalition forces accuse the Iranians of gun-running.
No one can say for sure which is ultimately true, but the blockade has largely held and prevented quantities of game-changing weapons from entering the country.
Saleh built up an impressive weapons stockpile over the years that included missiles, and those fired into Saudi Arabia earlier in the week may indeed have been locally manufactured, as the Houthis contend, despite U.S. and Saudi allegations to the contrary.
While the Houthis and Iran briefly operated direct flights between their capitals at the beginning of the war, no such route exists today, making any potential Iranian resupply efforts extremely difficult. Tiny sailboats may be able to smuggle small parts like guidance systems via costal routes, however.
EDITOR'S NOTE: Associated Press correspondent Brian Rohan has reported from the Middle East since 2011.
Follow Brian Rohan on Twitter at: www.twitter.com/brian_rohan