Diplomats in the 19th century were aristocrats. Their embassies were palaces and villas in the smartest parts of Paris and Vienna, Berlin, St Petersburg and London, houses where kings and princes might sleep and entertain. In the 20th century, embassies in many capitals still exuded magnificence but became, behind their facades, mere offices - for issuing visas, for promoting trade. In the 21st century, the institution has changed again. Today, the embassies of some countries, notably those of the US and UK, constitute a series of very grand and prestigious military targets scattered around the world. In London, the United...