The final weeks of the First World War saw a revolutionary upheaval in Europe as old empires collapsed and new, self-proclaimed 'nation-states' emerged in their place. For its advocates, the Yugoslav state created in 1918 represented a largely uniform culture and identity. But as its official name-the Kingdom of the Serbs, Croats and Slovenes-suggested, its population was by no means homogeneous and Britain, who had been instrumental in the birth...