The U.S. Central Command on Tuesday released video of overnight U.S. operations in Syria. The military airstrikes included the use of Tomahawk cruise missiles launched by the Navy from the Persian Gulf and the Red Sea. (U.S. CENTCOM)

The four Persian Gulf nations whose warplanes flew in concert with U.S. jets over Syria this week have spent the past few years acting with far less harmony, riven by divergent approaches to address the growth of Islamist political movements in the Arab world.

The differences among the countries have grown so stark and acrimonious that earlier this year, Saudi Arabia, the United Arab Emirates and Bahrain withdrew their ambassadors from Qatar, which has funded Islamists across the region to the consternation of the other three nations. In the months that followed, they have continued to wage a proxy war of sorts in Egypt and Libya, where the UAE recently conducted airstrikes against rebels backed by Qatar.

Qatar’s neighbors accused it of bankrolling terrorists. Qataris accused their neighbors of supporting strongmen who subvert the will of the people.

But with the Islamic State waving its black flag at the gates of Baghdad, Persian Gulf nations have decided to set aside their differences.

“Radical Islam is a profound threat to us and our values,” said Yousef al-Otaiba, the UAE’s ambassador to the United States. “We need to confront it as a team.”

As the war against the Islamic State expands with airstrikes in Syria, here's what senior national security correspondent Karen DeYoung, national security reporter Greg Miller, White House correspondent Katie Zezima and foreign-affairs writer Ishaan Tharoor have to say about what it all means. (Jason Aldag/The Washington Post)

The airstrikes in Syria were an unprecedented act of Arab military cooperation that involved Saudi Arabia bombing fellow Sunni Muslims, the launching of U.S. F-22 Raptor warplanes — employed in combat for the first time — from a base in the UAE, and the Royal Bahrain Air Force flying its inaugural combat missions.

“This was — and we hope will continue to be — a remarkable act of partnership among our allies in the gulf,” said a senior U.S. military official, speaking on the condition of anonymity because he was not authorized to discuss the operation.

The militants have seized the key Iraqi crossing to Jordan, and the Islamic State’s leaders have expressed a thirst to charge a few hundred miles south through the desert to the Saudi holy city of Mecca and eventually impose their harsh brand of Islamic law from the Mediterranean Sea to the Indian Ocean. Even though Qatar, Bahrain and the UAE do not face the same immediate risks as Jordan and Saudi Arabia, an incursion onto Saudi soil could spark fear and unleash economic turmoil on the peninsula.

The Islamic State “represents a real and present danger” to the four countries and to Jordan, which also joined in the military operation, said Theodore Karasik, the director of research at the Institute for Near East and Gulf Military Analysis in Dubai, the UAE’s largest city. That threat, he said, has been deemed by the countries “to be greater than what was happening among them.”

Several of the nations had sought military intervention against the Islamic State well in advance of President Obama’s decision to act. In private conversations with U.S. diplomats and military officials, Arab leaders conveyed a desire for a hard line against the militants weeks before the beheadings of two American journalists, which fueled opprobrium among the American public and led to new pressure on the White House.

As Secretary of State John F. Kerry traveled through the region last week to assemble the coalition, U.S. and Arab officials said his principal task was not to convince some of the countries of the need to act, but to coordinate their efforts.

“It is the coalition of the more willing than we are,” said Will McCants, the director of the Project on U.S. Relations with the Islamic World at the Brookings Institution in Washington. “They’ve been begging the United States to take this leadership role for a while.”

The countries did not want to act without the United States in the lead. They deemed U.S. firepower, intelligence and airborne coordination vital to the success of an air war in Syria, the U.S. and Arab officials said.

The U.S. military official noted that all five countries regularly train with the U.S. military and practice raids similar to those that were conducted on what was Tuesday morning in Syria. The allies flew U.S.-made fighter jets and dropped U.S.-manufactured munitions on targets selected by the U.S. military.

Qatar’s willingness to participate took some of its neighbors by surprise, but they nonetheless welcomed it, the officials said. Although Qatar’s support of Syrian opposition groups linked to the Muslim Brotherhood across the region has upset its neighbors — and led, in part, to the diplomatic breach — the Qatari government has insisted that it does not directly support the Islamic State; U.S. officials, including Kerry, have said they have no evidence to the contrary.

Of larger concern to the UAE and Saudi Arabia has been Qatar’s support for the Muslim Brotherhood in Egypt, including the former government of Mohamed Morsi, who was deposed by a military coup. The military chief who led the operation, Abdel Fatah al-Sissi, now presides over a government that has received generous financial support from Saudi Arabia and the UAE.

The UAE and Saudi Arabia have also been angered by Qatar’s support for a Libyan opposition group that seized the airport in the capital, Tripoli, and has established a rival government to the country’s elected parliament.

“There was very little trust among them,” McCants said of the gulf nations. But the Islamic State was an enemy “they all could agree upon.”

While U.S. military and diplomatic officials are pleased with the cooperation thus far, they note that the most critical regional contributions have yet to come: a Saudi promise to establish training facilities for moderate Syrian rebels, bases for them in Jordan, participation of special-operations ground forces from some of the nations, and more-aggressive steps by Qatar and other nations to target their citizens who seek to send funds to the Islamic State.

Those commitments “can change facts on the ground in ways that airstrikes will not do,” said James Stavridis, a former Navy admiral who served as supreme allied commander in Europe and now heads the Fletcher School of Law and Diplomacy at Tufts University. “The real value will be in what ultimately hits the table.”