By Stephen Kalin and William Maclean
DUBAI, June 19 (Reuters) - Two years after launching headfirst into a conflict in Yemen that has no end in sight, Saudi Arabia and the United Arab Emirates have astonished the world again, this time with a severe boycott of neighbouring Qatar.
Like the Yemen war, which has killed more than 10,000 people, the rift with Qatar is most closely associated with a new generation of leaders in the energy-rich Gulf who are more hawkish than conservative predecessors given more to cautious, consensual policymaking.
While the dispute could end up costing Qatar dearly, it also has implications for the Saudis and Emiratis whose activism, critics say, is fuelling uncertainty in an already unstable neighbourhood and could even push the region towards all-out conflict with arch-enemy Iran.
Saudi Arabia, the UAE, Bahrain and Egypt cut diplomatic and commercial ties with Qatar two weeks ago, accusing it of supporting terrorism, meddling in other countries' affairs and cozying up to Iran, all of which Qatar denies.
Mediation efforts, including by the United States, have been fruitless.
The new muscular policy is embodied in two powerful young leaders: 31-year-old Saudi Deputy Crown Prince Mohammed bin Salman and Sheikh Mohammed bin Zayed al-Nahyan, the 56-year-old crown prince of Abu Dhabi.
They stand in contrast to previous Gulf Arab leaders who over decades weathered crises mostly by time-consuming conciliation.
Their rival is also young: Qatar's ruling Emir Sheikh Tamim bin Hamad al-Thani took over from his father in 2013 at 33, inheriting a high-profile foreign policy that has seen his rich but tiny country exert outsized influence in the region.
"The rules of the game seem to have changed. The values governing interfamilial relations in the Gulf have changed," said Mamoun Fandy, a London-based political analyst.
"We are now talking about young people. I don't think it will get resolved soon."
PRINCE MOHAMMED, SHEIKH MOHAMMED
Saudi Arabia's Prince Mohammed, widely referred to as "MbS", runs economic, defence and oil strategy and has a direct line to the king, his 81-year-old father. In a kingdom ruled by six brothers in succession, he and his cousin the crown prince are the first from a new generation to reach the highest ranks of power in 64 years.
He is spearheading an ambitious drive to reform the kingdom's oil-dependent economy and led the charge into Yemen in 2015 to oppose a takeover by Iran-aligned fighters from the Houthi movement.
But after months of bombings, no side has emerged dominant in a war that has displaced more than three million people, left many on the edge of starvation and allowed a powerful al Qaeda branch to expand its operations.
Now MbS appears to have orchestrated the Qatar move just days after pulling off a summit in Riyadh where U.S. President Donald Trump called for bold action.
"It has his emerging hallmark of action that is sudden, spectacular but not necessarily strategic," said Jane Kinninmont, a Middle East expert at Chatham House. "It is a maximalist position without a clear endgame."
"MbS" gets on well with Abu Dhabi's Sheikh Mohammed, the deputy supreme commander of UAE armed forces, who is known as "MbZ". The Saudi prince's entourage happily concedes they see much to emulate in the UAE's successful diversification of its economy beyond oil.
MbZ has long espoused a hard line against Qatar and Iran, which seems to be rubbing off on MbS, who has ratcheted up the rhetoric. Last month MbS ruled out dialogue with Iran and pledged to protect Saudi Arabia from what he called Tehran's efforts to dominate the Muslim world.
In blunt remarks, he said any struggle for influence between the Sunni Muslim kingdom and the revolutionary Shi'ite theocracy ought to take place "inside Iran, not in Saudi Arabia".
Following twin attacks in Tehran earlier this month for which Iran's Revolutionary Guards blamed Saudi Arabia, Iran's foreign minister called those comments "a direct threat and a dangerous provocation".
Riyadh and its allies "are no longer risk averse," Chas Freeman, former U.S. Ambassador to Riyadh, said. "They were prudent, cautious to a fault. Now they are prepared to throw their weight around."
Qatar's ruler Sheikh Tamim weathered a smaller dispute with Gulf neighbours in 2014. He pledged to distinguish himself from his more overtly anti-Saudi father, Sheikh Hamad bin Khalifa al-Thani, who took power in a palace coup in 1995 and crafted Qatar's independent-minded foreign policy before stepping down in favour of his young son four years ago.
But Sheikh Tamim has continued to embrace maverick positions, cultivating relationships with Islamist movements like the Afghan Taliban and Palestinian Hamas in pursuit of leverage.
Saudi Arabia and its allies appear willing to use all means short of armed force to rein in Qatar, but the brittle mood has stirred worries about the possibility of violence.
Over the decades, Gulf states have sparred among themselves, mostly rhetorically, over border demarcation or foreign policy. In 1992, clashes on the Saudi-Qatari border led to several deaths.
This time, say analysts, Riyadh and Abu Dhabi are unhappy with what they consider the continued influence of Sheikh Hamad, including at Al Jazeera, the pan-Arab satellite TV network they accuse of interfering in other countries' affairs.
If Sheikh Tamim gives too much ground, he could face a challenge from inside his family. But if he remains defiant, royals may start grumbling as well.
"That might look less like a coup than a disgruntled board changing a CEO who is no longer making the company profits," said a Western diplomat in the region.
Riyadh and Abu Dhabi say they have made clear what they expect of Doha, but it is far from certain that Sheikh Tamim will simply comply. Unlike Yemen, already desperately poor before the war, Qatar is plugged into the global economy, with the world's highest income per capita.
The top liquefied natural gas exporter hosts the region's biggest U.S. military base, and boasts investments that include the Empire State Building, the London Shard and Harrods.
Transit disruptions pose a major threat to business, and there is even some talk that the boycott could eventually target Qatar's hosting of the 2022 World Cup.
"The unintended consequences of this can go out of control," said Fandy, the analyst. "It serves no one's purpose that this is pushed to its limits."
(Additional reporting by Sami Aboudi, Katie Paul, Sylvia Westall; editing by Peter Graff) ((email@example.com; +971 52 322 9759; Reuters Messaging: firstname.lastname@example.org))