DUBAI, United Arab Emirates -- The decision by four Arab nations to cut ties with Qatar marks the culmination of years of tension among a historically tightknit alliance of energy-rich Gulf Arab states that share borders, a common heritage and a strong alliance with Washington.
The move reflects longstanding anger at Qatar's support for Islamist groups that are outlawed as terrorist organizations by other Arab nations, as well as the increasingly bitter rivalry between Saudi Arabia and Iran.
How severe the impact will be on Qatar, which hosts the region's main U.S. military base used to launch strikes on the Islamic State group, depends on what further measures will be taken.
Analysts say U.S. President Donald Trump's recent visit to Saudi Arabia emboldened hawkish Saudi royals by positioning America squarely with Sunni Arab countries against Iran.
Here's a look at the issues:
------
WHY IS THE LITTLE PENINSULA NATION OF QATAR IMPORTANT?
Qatar is home to the forward headquarters of the U.S. military's Central Command. Its al-Udeid Air Base serves as a launching pad for coalition jets bombing IS sites in Iraq and Syria. The country has only around 270,000 citizens, but is the world's biggest producer of liquefied natural gas, sharing a vast underwater field with Iran.
Qatar also plays a role in talking to and bargaining with groups that many governments keep distance from. It helped free members of its own royal family from captivity by Shiite militants in Iraq in April. Reports emerged that Qatar paid hundreds of millions of dollars for their release, including to an al-Qaida offshoot in Syria -- and it secured the release of hostages in Syria's civil war, including 13 Greek Orthodox nuns held by an al-Qaida affiliate. Qatar has also hosted talks between the Taliban and Afghan government.
It took a major gamble on the Muslim Brotherhood, supporting its brief stint in power in Egypt as well as the group's Islamist offshoots in the region, including Hamas, which rules the Palestinian Gaza Strip. Qatar also once had open ties to Israel.
These activities, coupled with its popular Al-Jazeera news network, built Qatar's reputation of punching above its weight.
------
WHY IS QATAR AT ODDS WITH THE ARAB WORLD'S MOST POWERFUL COUNTRIES?
Tensions between Qatar and Saudi Arabia -- a Middle East heavyweight and the Gulf's anchoring state -- bubbled to the surface two weeks ago when Qatar said its state-run news agency and its Twitter account were hacked to publish a fake story claiming the emir, Sheikh Tamim bin Hamad Al Thani, had called Iran "a regional and Islamic power that cannot be ignored."
State-linked media in the region ignored Qatar's denial and continued to report the comments, while Saudi Arabia, the United Arab Emirates, Bahrain and Egypt blocked access to Al-Jazeera and affiliated sites. State-linked Saudi media launched an aggressive campaign accusing Qatar of supporting terrorist groups like al-Qaida and the Islamic State, destabilizing the region and stabbing its allies in the back. Some Gulf news coverage seemed to support regime change in Qatar as well, and accused its emir of holding a secret meeting with Iranian Revolutionary Guard commander Gen. Qassem Soleimani.
The UAE had long been angered by Qatar's support for Islamists in the Gulf and in Libya, and Saudi Arabia and Egypt view the Muslim Brotherhood as a threat. Saudi Arabia accuses Qatar of supporting "the activities of Iranian-backed terrorist groups in the Qatif province of Saudi Arabia and in neighbouring Bahrain" -- and of backing the Yemeni rebels its coalition is fighting.
------
WHAT ARE THE BROADER CONSEQUENCES?
There could be long-term economic consequences for Qatar, which would affect the millions of migrant workers and expatriates living there.
Saudi Arabia gave Qatari residents 14 days to leave and ordered its citizens not to reside, visit or transit through Qatar. Saudi Arabia, the UAE, Egypt and Bahrain have already suspended diplomatic ties with Qatar, which is pulling its troops from the Saudi-led Yemen war. Egypt and Saudi Arabia closed their airspace and sea traffic to Qatar -- a decision that targets Qatar Airways, one of the region's busiest carriers. The UAE's Etihad Airways, FlyDubai and the Middle East's largest carrier Emirates have suspended flights to Qatar.
U.S. Secretary of State Rex Tillerson has called on the parties to sit down and address their differences, while insisting the crisis will not affect the war against the Islamic State group.
------
MIGHT QATAR GIVE IN?
Qatar denies it supports terrorist groups in Syria or elsewhere, despite aggressive efforts to back Sunni rebel groups fighting to oust the Syrian government. The issue appears to be funding that goes through the country, and in principle that could be addressed.
But for now Qatar's ruler appears unfazed. Qatari media published a cartoon mocking Saudi King Salman for spreading "fake news" and last week the emir called Iranian President Hasan Rouhani to congratulate him on his re-election -- a clear and public rebuttal of Saudi Arabia's efforts to force Qatar to fall in line.
Qatar's emir, believed to be just 37 years old, could retaliate by withdrawing from the six-nation Gulf Cooperation Council and redraw alliances to snub Saudi Arabia's 31-year-old Deputy Crown Prince Mohammed bin Salman and Abu Dhabi's Crown Prince Mohammed bin Zayed, who are believed to be the two main figures orchestrating the standoff.
Three years ago, several Gulf states withdrew their ambassadors from Qatar for nine months over the country's support for the Brotherhood. The details of the agreement that ended that standoff were never made public, but it included promises that Qatar would end its support for the Brotherhood and scale back Al Jazeera's Brotherhood coverage. Since the demands made now of Qatar are also somewhat hazy, some version of this scenario could recur.
