Europe responded with a mixture of panic, disorientation and frantic steps to limit the damage after the resignation of US defence secretary James Mattis.
Mr Mattis's decision to quit the administration came after the US president Donald Trump confirmed he is ending all US military operations in Syria, and amid reports he is planning to halve the US troop presence in Afghanistan.
The resignation of Mr Mattis deprives Europe of one of its most reliable interlocutors and a firm supporter of the Nato transatlantic defence alliance.
There are no vacuums in foreign policy, certainly not in the Middle East. In a fragile region every action is a catalyst for another. If allies cannot be relied upon, others are sought to take their place. Jim Mattis understood - vital any successor agrees. https://t.co/ED1sfpys5Y
— Alistair Burt (@AlistairBurtUK) December 21, 2018
Mr Mattis’s resignation is seen in Europe as an alarming symbol of Mr Trump’s determination to take personal charge of foreign policy, and the pointed reference in his resignation letter to the need to treat allies with respect will be noted.
UK defence and foreign office ministers, habitually inclined to keep differences with the US out of public sight, openly clashed with Mr Trump's decision. The UK Middle East minister Alistair Burt tweeted: "There are no vacuums in foreign policy, certainly not in the Middle East. In a fragile region every action is a catalyst for another. If allies cannot be relied upon, others are sought to take their place. Jim Mattis understood – vital any successor agrees."
The tweet is a warning to the US that the Gulf states, as well as the Kurds, may deduce that the US pullout means its long-term interests may lie in allying with other more steadfast partners such as Russia or China.
Germany, the country that had most to benefit from an agreed political settlement inside Syria in terms of returning refugees, also insisted the security threat posed by Islamic State was alive.
"The IS [Islamic State] has been pushed back, but the threat is not over. There is a danger that the consequences of [Trump's] decision could hurt the fight against the IS and endanger what has been achieved," said German foreign minister Heiko Maas in a statement.
The sense of a profound transatlantic crisis spread across the European foreign policy establishment. Co-chair of the European Council on Foreign Relations Carl Bildt tweeted: "A morning of alarm in Europe. Sec Def Mattis is the remaining strong bond across the Atlantic in the Trump administration. All the others are fragile at best or broken at worst."
Turkish troops
French president Emmanuel Macron was discussing with allies whether a supported French presence could act as a temporary substitute for the departing American ground troops in Syria.
Attempts were also being made to discover how quickly the 2,000 US troops in northeast Syria were leaving, and, separately, how speedily Turkish troops under the instruction of their president Recep Tayyip Erdogan plan to go over the border into Syria to attack what Ankara regards as Kurdish terrorist havens.
The sense of anger, edging on defiance, at Mr Trump’s decision was clearest in Paris.
French defence minister Florence Parly said on RTL radio: “We do not share the analyses that the territorial caliphate [of Islamic State] has been annihilated. It’s an extremely grave decision, and we think the job must be finished. While the territory controlled by the caliphate is no longer what it was in 2014 . . . if it has been reduced to near nothing, there remains, however, a pocket where jihadists have bunkered down,” she said.
Ms Parly also suggested that implementing the withdrawal of 2,000 US soldiers from Syria should be discussed among the allied coalition, adding that “you can’t withdraw troops from one day to another”.
French forces
Mr Macron has invited two leaders of the Kurdish-dominated Syrian Democratic Forces (SDF) to Paris to discuss how to protect the Kurds from what may now be an attack either by Islamic State, Turkish forces or Syrian government forces.
France has about 1,100 troops in Iraq and Syria, providing logistics, training and heavy artillery support, as well as fighter jets. In Syria it has dozens of special forces, military advisers and some foreign office personnel.
Mr Macron spoke with Mr Trump on Tuesday night, diplomats said.
"The military campaign against Islamic State continues," French army spokesman Patrik Steiger told a news conference. "At this stage, the announcement by the American president has no impact on France's ongoing participation [in the coalition]." – Guardian