It's happening in Iraq and Iran, but right now the main hotspot is Yemen, the poorest country on the Arabian peninsula, wracked by tribal insurrection, southern secessionists and a resurgent al-Qaida.
Things are so bad in Yemen, the most populous country on the peninsula, that it is in danger of collapsing as a state with its wars and insurrections spilling over into Saudi Arabia, the world's largest oil producer.
The Saudis have backed Yemen's beleaguered president, Ali Abdullah Saleh, in his five-year war with Shiite Zaidi rebels in the unruly north, centered on Saada province.
His government in Sanaa says the tribesmen are backed by Shiite-dominated Iran, Saudi Arabia's main rival in the oil-rich Gulf, and its proxies in Iraq and Lebanon.
Tehran denies that. But Sunni-dominated Yemen said in August that it had captured Iranian-made arms, including machine guns and battlefield rockets, from the rebels and intercepted a boat carrying six Iranians, possibly agents or military instructors, off Yemen's coast.
According to Arab officials and Western intelligence sources, the Saudis, who don't want Iran stirring up trouble on their porous southern flank, have been financing Saleh's counterinsurgency campaign to the tune of millions of dollars a week.
There have been repeated reports, largely from the northern rebels who are known as al-Houthis after the clan leading the rebellion, that the Saudi military is aiding Saleh's poorly trained and badly equipped forces with airstrikes against rebel strongholds along the mountainous border.
On Oct. 19 the insurgents claimed Saudi ground forces in the Hasama border region bombarded the main market town with machine gun and mortar fire. Authorities in Sanaa deny any Saudi involvement.
According to Texas-based security consultancy Strategic Forecasting, "Yemen and Saudi Arabia are now seeking out mercenaries, particularly from Ukraine, to fly Yemen's Soviet-era MiGs and Sukhois in hopes of regaining the upper hand against the al-Houthis and their Iranian backers in this proxy war."
Saleh's forces, ill equipped and poorly paid, have fared badly against the rebels since he launched a major scorched-earth offensive against the al-Houthis in August, supposedly on the ground they broke a cease-fire agreement but more likely because Saleh feels a need to assert his authority as the state falls apart.
In those circumstances, Saudi backing is vital if he is to cling to power and ensure that his son Ahmed, a general who commands the army's special forces, is to succeed him.
Egypt, another Sunni-led Arab state that opposes Shiite Iran, is also reported to be aiding Saleh with arms shipments. According to Strategic Forecasting, "The Egyptians are pushing for sustained airstrikes in … Saada province, greater U.S. assistance and replacement pilots for Yemen's air force.
"The Saudi leadership is expected to consult with the United States on the matter, but efforts already appear to be under way to place more capable pilots in Yemen's combat jets."
A failed attempt by a Yemeni al-Qaida operative to assassinate the Saudi prince who heads the kingdom's counterinsurgency campaign in the Red Sea port of Jeddah on Aug. 17 heightened alarm in Riyadh about the prospect of Yemen falling apart.
The Saudis fear that al-Qaida, which has been rebuilding its forces in eastern Yemen after its campaign in Saudi Arabia was crushed in 2006-07, would exploit the chaos to launch a new offensive against the al-Saud monarchy.
The Saudis also seem to be taking a tougher line over Iran. The disappearance and possible defection of an Iranian nuclear scientist in Saudi Arabia in early June was the first known incident of its kind to occur in the kingdom.
It pointed to a possible joint operation between Saudi intelligence and the U.S. Central Intelligence Agency to get their hands on an Iranian with inside knowledge of Tehran's reported drive to acquire nuclear weapons.
If so, that would be a first. Saudi intelligence, which played a key role with the CIA in arming Islamist guerrillas against the Soviets in the 1979-89 Afghan War, is also now reported to be aiding dissident forces inside Iran to counter Iranian encroachment in Iraq as U.S. forces withdraw.
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