* Gulf-backed forces pushing from Marib towards capital Sanaa
* Tribal, sectarian and regional allegiances key
* Many fighters in Marib appear loyal to Islah Islamist party
* Next advance may come in al-Jawf province
By Angus McDowall
MARIB, Yemen, Oct 21 (Reuters) - Mohsen Saleh al-Muradi does not just want to drive the Shi'ite Houthi fighters out of Yemen's capital 130 km (80 miles) from his home town, he wants to hunt them down and stamp them out.
"I will keep fighting all the way to Maran," said the slight, moustached native of the north Yemen town of Marib, wearing a bright red headscarf and a bullet pouch on his chest, referring to the Houthis highland stronghold.
"I want to trample them under my feet."
In a messy conflict of many fronts, the forces backed by wealthy neighbouring Gulf states against the Houthi fighters that control Sanaa often have little in common with each other and scant enthusiasm for the leader on whose behalf they are ostensibly fighting: President Abd Rabbu Mansour al-Hadi.
What they increasingly share is a visceral sectarian hatred for Shi'ites, a dangerous new trait in a country where different interpretations of Islam co-existed for centuries.
The Houthis fought for two decades on behalf of the Zaydi Shi'ite sect which ruled a kingdom in north Yemen for 1,000 years until it was toppled in a military coup in 1962.
Since last year Houthi fighters emerged as the most powerful force in the country, after forming an alliance with their former nemesis, ex-President Ali Abdullah Saleh, himself born a Zaydi but long a leader of the republican political establishment opposed to the old monarchy.
In Marib's market, the different backgrounds of the hundreds of armed men who said they had come there to fight against the Houthis shows the complexities of a war in which Yemen's old tribal hierarchy and its sectarian harmony have eroded.
Some were from the Red Sea coastal plain of Tihama and its terraced mountain hinterland of Jebel Raymah, others had come from Sanaa, from the northern highland areas of Hajjar and Amran, or from Dhamar, a city in Yemen's central plateau.
What united them was vehement anger at Saleh, the Houthis and their presumed Shi'ite ally Iran. Many described the militia using the highly sectarian anti-Shi'ite term "rejectionists". The Houthis, for their part, typically accuse all their Sunni foes of supporting Islamic State.
"The Houthis weren't here before. But they want the whole country. The problem is their religion. It comes from Iran," said Ahmed, a soldier from the Red Sea, mostly Sunni, city of Hodeida. He was wearing a uniform provided by the Saudi-led coalition of Arab countries, who joined the war in March and have helped drive the Houthis from Aden in the south.
A percussive boom rolls over Marib from rugged mountains to the west, in what is likely to be the next pivotal battlefield as the anti-Houthi fighters try to close in on Sanaa. They are now fighting in the Sirwah region, but may soon move north through al-Jawf, the fighter said.
The war will dictate who rules Yemen, whether it remains a single country and the prospects of ending a human crisis affecting millions in one of the poorest Arab states.
It has also become the latest theatre in a wider regional rivalry between Sunni Saudi Arabia and Shi'ite Iran, whose proxies and allies have killed hundreds of thousands of people in civil wars in Iraq and Syria.
LITTLE TRADITION OF HATRED
The sectarian hatred that has consumed much of the Middle East in recent years has traditionally been unheard of in Yemen.
Between a fifth and a third of Yemenis are Zaydis, belonging to an ancient branch of Islam that is grouped with Shi'ites because of the side its followers took in a 7th century dispute over the succession to the Prophet Mohammad.
But unlike the branch of Shi'ite Islam that later became Iran's state religion, Zaydis never developed major doctrinal differences with mainstream Sunni schools. Many of north Yemen's big tribes have long followed both Zaydi and Sunni Islam without controversy.
A civil war in the 1960s was fought not on sectarian lines, but between supporters of the old Zaydi monarchy, backed by Sunni Saudi Arabia, and republicans aided by Egypt. When the republicans won, some top tribal leaders embraced Sunnism as a way of diminishing the influence of the Zaydi old guard.
During his nearly three decades in power, Saleh played down his own Zaydi background, as did other members of the tribal elite that backed him.
From the 1970s onwards, a more explicitly sectarian element was introduced as migrant Yemeni workers in Saudi Arabia embraced its rigid Wahhabi Sunni doctrine, often in response to the stultifying social hierarchy of Yemen's old monarchy.
The Saudis, for their part, started a decades-long policy of buying influence in Yemen by distributing patronage to northern tribal sheikhs, and lavishing money on Wahhabi mosques.
Saleh aided the rise of Sunni militant sentiment by cutting a deal with returning veterans of the 1980s jihad against the Soviets in Afghanistan. He recruited Sunni militants to help fight against Communist and Socialist separatists in the south.
Opponents of the Houthis accuse them of seeking to revive the monarchy and promote Iranian influence. The Houthis deny this, casting themselves as a nationwide revolutionary organisation, fighting corruption.
THE ONE WITH THE MONEY CAN WIN
Still, the war has yet to be reduced to a straightforward conflict between Sunnis and Shi'ites, like those that have unleashed bloodbaths from Damascus to Baghdad.
In the mainly Sunni south, many of Hadi's supporters are driven more by regional separatism than sectarianism, though the area does include entrenched Sunni militant groups that have called for battle against the Houthis on religious grounds.
In the more religiously mixed north, many anti-Houthi fighters are followers of the Islah party, a political movement which includes Yemen's branch of the Sunni Islamist Muslim Brotherhood and Sunni leaders of historically Zaydi tribes.
Many of the Yemeni soldiers now opposing the Houthis fought against them when Saleh was in power, as members of the 1st Armoured Division led by General Ali Mohsen al-Ahmar, a senior Islah figure now in exile in Saudi Arabia. Marib's new governor, Sultan al-Arada, is an Islah leader, and the armed forces' Chief of Staff Mohammed al-Maqdisi is a party sympathiser.
Fuad Mohammed Ali Marhabi, a 26-year old veteran of the 1st Armoured Division from Sanaa, now serving in an army uniform provided by the Saudis, says the new battle is a continuation of the old fight: "That was our war. It was against the Houthis. Now we are fighting them again," he said.
The key to the capital is winning the allegiance of tribes in the area. But six months since the Gulf countries joined the conflict, they have yet to secure reliable tribal support.
"There's no neat division of tribes. Families will back both sides to ensure they have somebody on the winning side," said Adam Baron, a visiting fellow of the European Council on Foreign Relations. "It makes it very hard for the Saudis to figure out who to empower with money and arms."
A soldier at the Saudi air base in the border town of Sharura, deep in the Empty Quarter desert and a main supply route across the open dunes to Marib 400 kilometres away, said winning the support of tribes would require spending money.
"The one with the money can win in that area," he said, standing by a wall map showing Houthi positions in large scale. "You can buy loyalty." (Editing by William Maclean and Peter Graff)
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