The Saudi Arabian-led intervention into Yemen’s civil war Thursday was remarkable for both the size of the coalition involved and the speed with which the plan coalesced. The U.S., which withdrew its last special operations forces from Yemen over the weekend, had only a brief warning that Saudi airpower was about to be unleashed.

U.S. and Arab officials tell us that the tripwire for the military action was Iranian-backed Houthi rebels storming the Yemeni port city of Aden, where President Abdurabuh Mansur Hadi had taken refuge earlier this month. On Thursday, Egyptian warships entered the Gulf of Aden, a strategic water route between the Red and Arabian Seas, while Saudi jets pounded Houthi positions on the mainland.

Yemen’s Fault Lines

America’s traditional allies in the Middle East — Saudi Arabia, Kuwait, the United Arab Emirates, Turkey and Egypt — began stitching together the military coalition in the beginning of March, according to sources familiar with the negotiations. The Saudis, however, did not begin having detailed, top-level discussions with the Obama administration on how the U.S. could support the new alliance until Sunday, U.S. officials tell us.

Bernadette Meehan, the spokeswoman for the National Security Council, said Thursday: “For days before the offensive, the Saudis and other Gulf partners were communicating with us about the types of options they were considering, including military action.”

Saudi Arabia’s ambassador in Washington, Adel al-Jubeir, supported Meehan’s characterization. “We have been discussing this matter with the United States in principle for many months,” he told CNN Thursday. “We have been discussing this matter in more detail as the time approached and the final decision to take action didn’t really happen until the last minute, because of circumstances in Yemen. So the U.S. had visibility in terms of our thinking and we coordinated and consulted closely with the White House on this.”

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Not everyone agrees with that timeline. At a Senate Armed Services Committee hearing on Thursday, General Lloyd Austin, head of the U.S. Central Command, said he did not learn the Saudis were actually going attack Yemen until an hour before the operation was launched. Austin, whose theater includes Yemen, would normally expect to be given more than an hour’s heads-up before such a military operation. Another official with Centcom, who asked not to be named, told us Thursday evening that Austin had “indications” over the weekend that something might happen but got no final confirmation until Wednesday.

Saudi officials who briefed U.S. lawmakers on Thursday said that planning for the coalition began about three weeks ago, following the visit of Turkish President Recep Tayyip Erdogan to Saudi Arabia. During those meetings, Erdogan was apprised of potential military action in Yemen and agreed that Turkey would support it.

Not surprising, then, that on Thursday Erdogan announced Turkey’s approval and said his nation might even provide logistical support. “We support Saudi Arabia’s intervention,” he told France 24 in an interview. “Iran and the terrorist groups must withdraw.”

More details of the planning for the operation came Thursday in anArabic-language tweet from the United Arab Emirates’ foreign minister, Anwar Gargash. He tweeted: “The decision to engage in Operation Storm of Resolve was not made hastily, it was preceded by intense political negotiation, effort and initiatives to counter the Al Houthi group. This Operation came after the UAE ‘knocked on all the doors.’ ”

The coalition was ultimately cemented, according to Arab diplomats and U.S. officials, over the weekend at a meeting in the Saudi capital of Riyadh, involving senior officials from Kuwait, Saudi Arabia, the United Arab Emirates, Qatar and Bahrain. The Saudi press at the time reported that the conference was to discuss the crisis in Yemen, but gave no indication that military force was being considered.

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While some details of the planning remain hazy, one thing is clear: the Saudi initiative is a major step in the new Middle Eastern Cold War, pitting America’s traditional Arab allies against Iran. It’s a convoluted situation, and has resulted in a confusing American regional policy. On one hand, President Barack Obama is urgently trying to close a nuclear framework agreement with Iran this weekend in Switzerland. Yet Saudi Arabia and its Sunni Arab neighbors are wary of that deal, particularly in light of Iran’s role in supporting their adversaries in Lebanon, Iraq, Syria and Yemen.

In Yemen, Obama is now aiding the fight against the Houthi militias supported by Iran. (U.S. officials tell us that the U.S. military is now supporting this Saudi-led campaign by providing refueling for Saudi jets and overhead imagery from drones and satellites.) At the same time, in neighboring Iraq, U.S. aircraft began strikes to support Iraqi forces closely tied to Iran now fighting against Islamic State in Tikrit. The apparent contradiction seems to be puzzling Iran and its allies as well: Some of the Iranian-backed Shiite militias announced they would stop fighting in Tikrit because of the U.S. airstrikes supporting them.

It’s also confounding some leading lawmakers. Senator John McCain, the chairman of the Senate Armed Services Committee, told reporters Thursday he didn’t think there was any U.S. assistance to the Saudi-led campaign. “These countries, led by Saudi Arabia, did not notify us nor seek our coordination or our assistance in this effort,” he said. “That is because they believe we are siding with Iran.”

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Simon Henderson, an expert on Gulf affairs at the Washington Institute for Near East Policy, told us that the new coalition-building for Yemen shouldn’t be seen as a failure of U.S. leadership but as a testament to the strength of America’s traditional alliances in the Middle East.

“This is a crucial example of the way America’s Arab allies want to coordinate between themselves and with Washington,” he said. “Despite the concern of Arab allies with the direction of diplomacy on the Iran nuclear issue, the Arab capitals know that they need to bring Washington into the loop.”

The question now is whether Obama’s support for America’s allies in Yemen will hamper the prospect of making Iran a new ally this weekend in the nuclear negotiations in Switzerland.