RIYADH/KUWAIT A breach between Qatar and some of its Gulf Arab neighbors is a pivotal test for a three-decade-old union of monarchies formed to stand united when threatened by common enemies.
The six neighbors have struggled for years to transform their alliance from a simple security pact into an integrated economy. But plans for a customs union, integrated power grids and a joint military command remain unfinished or unrealized.
Critics of the Gulf Cooperation Council (GCC) blame its inadequacies on petty jealousies, border disputes, or the perceived dominance of its biggest member, Saudi Arabia.
If the allies can no longer reach broad agreement on how to navigate the political troubles afflicting the region, then the main point of their partnership is in question, say analysts.
Born more out of fear than greed, the GCC, which also includes Kuwait, Bahrain, the United Arab Emirates (UAE) and Oman, has managed to present a united front at times of threat ranging from Iranian revolution to Iraqi invasion.
The club was born in 1981 to counter the revolutionaries who had toppled Iran's Shah, a fellow dynast familiar to Gulf Arab leaders, two years earlier. As Iran and Iraq embarked on an eight-year war, survival became the watchword for the GCC.
Now, even as most Gulf Arab economies are booming and the GCC touts itself as a rare outpost of stability in a turbulent region, the member countries have never appeared more divided.
"Will the GCC kill itself?" ran Thursday's headline in Kuwaiti newspaper Al-Rai.
Wednesday's statement by Saudi Arabia, the UAE and Bahrain that they were withdrawing ambassadors from Doha and all but accusing Qatar of undermining their internal stability was unprecedented as a public display of divisions.
Saudi Arabia and the UAE are incensed by Qatar's support for the Muslim Brotherhood, which they regard as a dangerous political enemy. They are also cross about Doha's backing for more radical Islamist groups in Syria.
The UAE summoned the Qatari ambassador in February after Qatar-based Brotherhood cleric Youssef al-Qaradawi condemned the UAE as was against Islamic rule, a remark the UAE described as insulting and shameful.
UAE media quoted Qatari Foreign Minister Khaled al-Attiyah as saying the comments did not reflect Qatar's views. Sources close to the cleric said he would not stop speaking his mind.
Qaradawi told Reuters Saudi Arabia was backing those who "are far from God and Islam" in Egypt - the military-backed authorities that overthrew an elected Islamist president.
Saudi Arabia and Qatar are leading backers of rival Syrian rebel groups, and they and other Gulf states are the principal external forces supporting key players in Egypt and Yemen.
Acting together they could effect regional change. Apart, they risk dragging the Gulf into the post-Arab Spring quagmire.
A Gulf Arab diplomat said the decision to recall the envoys was taken after a meeting of GCC foreign ministers on Tuesday at which it became clear Qatar would not change its approach.
"After this meeting they decided - the Saudis, the Emirates and Bahrain - to take this kind of step," the diplomat said.
"It is a very negative step in our experience as a group, in this organization."
There have been plenty of previous rifts among the six dynasties, which sometimes appear to regard each other as rivals rather than partners, but they have never involved such an airing of dirty linen or come at such a dangerous time.
Unlike in the past, the Gulf states cannot count on strong Arab allies with large armies to see off external threats.
Gulf citizens see their region as the last bastion of security in the Arab world, with Iraq and Syria in conflict, Yemen and Libya in chaos, Egypt destabilized and Lebanon and Jordan undermined by turmoil in neighboring states.
Critics of the GCC deride its failure to fulfill its promises, such as a currency or border union. Despite big arms purchases, all its members remain dependent for their defense on alliances with Western powers, principally the United States.
The Gulf countries refer to each other in official statements as "full brothers", the closest blood relationship in a society traditionally built upon large polygamous families.
But they have often nursed sibling rivalries in disputes ranging from border demarcation and foreign policy to occasionally unflattering portrayal of rulers in each other's state media.
Saudi Arabia and Qatar in particular have had a series of disputes, including border clashes in 1992 that led to several deaths and a five-year period from 2002 when Riyadh had no ambassador in Doha after arguments about al-Jazeera broadcasts.
Qatar and the UAE also fell out in the 1990s when Dubai gave refuge to a former Qatari emir who was ousted in 1995, and Doha has crossed swords with Bahrain. Smaller-scale rows have periodically flared up between Saudi Arabia, Oman and the UAE.
At root, these spats and the GCC's slow pace in creating a stronger union have often resulted from the fundamental imbalance among a group of countries in which Saudi Arabia has a bigger population than the other five combined.
Political analysts say some in the smaller countries have seen the GCC as a ratification instrument for Saudi policies.
"Becoming a mediating power in the region has upset a lot of governments who think we are too small. But we are here to say we are not small, we believe in our role and will continue it," said a source close to the Qatari government.
For Saudi Arabia in particular, the disunity is a source of frustration. Riyadh has pushed hard since late 2011 for the GCC to forge a closer union on a shared foreign and security policy.
The personal initiative of King Abdullah, the idea emerged as a response to the Arab Spring and fears of Iranian interference and represents an important building block of Saudi efforts to become less dependent on the West.
But in December Oman said outright it did not want to be part of such a union, weeks after angering Riyadh by facilitating secret U.S.-Iranian talks that the Saudis fear will reduce international pressure on Tehran.
Kuwait stayed above the fray this week, talking of acting as a mediator when its emir returns from a medical trip overseas, but refraining from joining the pressure on Doha.
"The Saudis are strongly committed to the unity of the Gulf states, and they want other states to take their share of responsibilities towards the people of the Gulf," said Saud al-Sarhan, director of research at the King Faisal Center for Research and Islamic Studies in Riyadh.
"Saudi Arabia is taking control of regional and Arab security, and slowly bringing to an end the era of reliance on foreign partners for strategic priorities," he added.
(Additional reporting by Amena Bakr in Doha and Rania el Gamal and Yara Bayoumy in Dubai; Editing by William Maclean and Andrew Roche)