On November 13, 1918 the Allied troops occupied Constantinople, the capital of the Ottoman Empire. The Ottoman Empire was the Caliphate, the Islamic State of its day.
Yes, but it was the secularizing Ataturk who abolished the Caliphate after the Allies were unwilling to fight for their partition rights in Anatolia and what became European Turkey. The Allies would have been wiser to allow the old Sultan to move to Damascus or inside the the French mandate or Baghdad in the British mandate and remain as Caliph. A tame Caliph would have been very beneficial and would have prevented Sunni Islam from becoming the hotbed of lunacy it became beginning in the 1920's.
And, until the New Turks with their modern-style Turkish nationalism got sway at the Sublime Porte (cf. the history of the Armenian genocide), the old Caliphs had been letting their Islamic state change in increasingly human ways: abolishing slavery, abolishing dhimmitude and making all citizens of the Empire formally equal before the law, regardless of religion (a concession for French and British support in the Crimean War), establishing a parliamentary constitution,...