Shashank Joshi, a fellow of the Royal United Services Institute, said: “The Gulf Arab political order for almost the entire post-war period has depended on US interest in the region.

“The monarchies endured for so long not because of any sort of popular legitimacy but because they could depend on enormous external support. Those regimes, which have already had to deal with a high degree of domestic mobilisation will come under unbearable stress and they cannot survive without the technical advantage of western weapons.”

Few are expecting the US Fifth Fleet to pack up and sail home in the immediate future, just because America has found enough oil and gas for its needs in its own back garden. Geopolitical change tends to lag a decade or two behind economic change, but as the US finds itself less reliant on regimes with which it has little in common there will be powerful pressure on the Pentagon to begin to bring home its troops and hardware.

The speed of US disengagement will depend to a large extent on whether the alternative is a vacuum and instability, as a variety of religious and tribal forces vie to inherit the Gulf kingdoms. The role of Iran, an economy largely dependent on oil sales that already faces severe budget shortfalls from sanctions, is likely to be critical. Whether it responds to crisis by collaboration or confrontation with its traditional Gulf adversaries will shape the region’s future.