Iron Kingdom, by Christopher Clark

Many states have been conquered, partitioned, occupied, "ended" and even destroyed. Prussia is unique in that it was formally abolished by decree of the British, American, French and Soviet victors in February 1947, after it ceased to exist in any meaningful sense. By then the heartlands of Silesia, Pomerania and East Prussia had been annexed by Poland and the Soviet Union, and ethnically cleansed of their German population, and the notorious "Junker" noble class systematically uprooted. It is a tribute to the enduring power of the "Prussian myth" that the victors felt the need to exhume the corpse, ram a final stake through its heart and bury it for good.

Christopher Clark begins Iron Kingdom, his history of "the rise and downfall of Prussia", with this famous decree, but his remarkable book is not another exorcism, nor an uncritical celebration. He provides a sophisticated yet accessible account of how a middling German dynasty manoeuvred its way into the European pentarchy of powers. For his Prussia is "self-made": through will-power, hard work and ingenuity, monarchy and administration fashioned out of the unproductive "sandbox" of Brandenburg and assorted territories a state able to sustain an army very much larger than its wealth or population warranted.

The key was the "governing compromise" by which the Prussian nobility traded political participation at the highest level and service to the state for socio-legal domination of their peasantry. This has been dubbed the "military-agrarian complex". Yet Prussia was the product not just of the graft of its princes but also the artifice of its myth-makers. As Clark expertly shows, the "Prussian virtues" of thrift, modesty and martial valour were carefully constructed and burnished.

If all this sounds grim, Prussia was also home to many of the most progressive currents in European history. It was a major centre of the European enlightenment: Frederick the Great maintained an animated correspondence with some of the greatest figures of the age, such as Voltaire. He famously announced that while he was a king in the cabinet, he was a philosophe in his study. More prosaically, 18th-century Prussia boasted the most comprehensive welfare system of any large state. Not only did the state protect peasant holdings from the encroachment of the aristocracy, it also maintained a system of granaries designed both for provisioning the army and for keeping down the price of bread in times of scarcity.

In short, Prussia was a land of paradox. The superb cover illustration, a mounted cavalryman observing an aircraft trial just before the First World War, captures this brilliantly. It evokes both the modernity and backwardness of Prussia, while the Darth Vader-like figure on the horse is both menacing and a little forlorn.

There were many reasons why Prussia was so special, but the greatest single factor was geography. Clark precedes his analysis with six maps, and introduces most of his chapters with a geopolitical account of the changing international situation. Like most European states, Brandenburg-Prussia started out as a medley of loosely connected and scattered territories. Unlike many, it was completely devoid of natural boundaries. The whole of Prussian history, therefore, was dominated by the search for security. Iron Kingdom masterfully traces the process by which the monarchy was territorially consolidated in fits and starts between the 17th and 19th centuries.

None of this was preordained, but contingent on the ebb and flow of the European state system and the skill of Prussian leaders. For this reason, the core of Iron Kingdom is a series of scintillating pen-portraits. The most vivid is that of chancellor Otto von Bismarck: the most radical Prussian geopolitician of all, who believed secure borders could only be achieved within the framework of a united Germany. In 1871, after having worsted the Danes, Austrians and French in a series of brilliant wars, Bismarck "subsumed" Prussia into the Second German Empire. The South German turkeys were persuaded to vote for Christmas.

That was the end of the sovereign Prussian state, but - as Clark shows - it left behind a powerfully ambivalent legacy. Prussia made up about 60 per cent of the new Germany, and Prussian "militarism" dominated the Germany of Kaiser William II and contributed to the catastrophe of 1914-1918. Many of those hostile to the new democracy of the Weimar Republic after the war were working to a traditional Prussian agenda. Even the Nazis sought to bask in the reflected glory of Prussia. Clark offers a superb reconstruction of the charade in the Garrison Church in March 1933, supposed to suggest a symbiosis between the "new" movement and the "old" Prussia. It was attended by two members of the former royal family, one in Nazi uniform.

Yet Prussia proved to be a "bulwark of democracy" during the Weimar Republic, where a Social Democratic state government held out after other regions had succumbed to the National Socialists. Moreover, the elite German resistance to Hitler was dominated by Prussians in the army and Foreign Office, many of whom used to meet at the Silesian estate of the von Moltke family. Many were butchered by the Gestapo after the abortive July plot. As Clark persuasively shows, Prussia and Prussianism were neither directly responsible for Hitler, nor can they be appropriated for the resistance, as apologists would have it.

The spine of this book is very much the high politics of foreign policy, and the domestic imperatives that resulted. But Clark has not straitjacketed himself: his account deals with different Prussias, including that of women, the family, the regions, and religious and national minorities. The author's empathetic embrace even extends to Poland, the quintessential 18th-century failed state, which Prussia helped to wind up.

Iron Kingdom wisely does not attempt draw any lessons. Yet the story of Prussia may tell us something. First, it is a reminder of the transformative and moral value of the state in welfare, education and commerce, so often demonised in Anglo-Saxon discourses, especially Cons- ervative ones. Secondly, the "Prussian path" to German unity beckons as both a warning and a navigation light to those contemplating further European integration. It provides a model of how unity can be created in very adverse circumstances. But which state will be Europe's Prussia, and who will be her Bismarck?

Brendan Simms teaches history at Cambridge; his books include 'Unfinest Hour: Britain and the destruction of Bosnia' (Penguin)