When the Saudi ambassador in Washington announced the launching of airstrikes and a military intervention in Yemen on Wednesday night, the kingdom surprised everyone - not least Iran.Conventional wisdom was that Riyadh had dithered and left it too late. The Houthis and elements of the army loyal to the ousted autocrat Ali Abdullah Saleh and his son Ahmed had advanced on the southern city of Aden with such speed that its fall, and that of President Abd Rabbuh Mansour Hadi, was considered only a matter of time.

John Allen, the retired marine general charged by US President Barack Obama to coordinate the campaign against the Islamic State (IS) group, is a man confident of his facts. Fresh from Turkey, which had just agreed to enter the air campaign against the militants, he told the Aspen Security Forum that IS are losing.