Q&A: Qatar's falling out with its Arab neighbors

A decision by four Arab nations to cut ties with Qatar marks the culmination of years of tension among a historically tightknit grouping 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 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. President Donald Trump tweeted Tuesday that Arab leaders complained about Qatar in his recent visit to Saudi Arabia. In his tweet, Trump did not take a position on the decision by Saudi Arabia and three other Arab nations to sever diplomatic relations with Qatar but appeared to suggest it was understandable.

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, home to the Al Jazeera news network, also plays a role in negotiating with groups that many governments keep distance from. It helped free members of its own royal family from captivity by Shiite militants in Iraq. It secured the release of hostages in Syria's civil war, including some held by an al-Qaida affiliate. Qatar has also hosted talks between the Afghan government and the Taliban. 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 Gaza Strip. Qatar also once had open ties to Israel.

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