Those who enjoy long history books and have a particular interest in German history, especially in the history of Prussia, will want to read “Iron Kingdom” (Harvard University Press, 775 pages, $35). And if none of the above applies, this book can still be read for sheer pleasure, with length entirely irrelevant because many will want to read it again. It is the pleasure of discovery that Christopher Clark offers in this account of the rise and fall of Prussia.

There is the black legend of a congenitally aggressive kingdom habitually led to war by bird-brained militarists. There are also inflated claims of high intellectual achievement and religious tolerance — yes, the emphatically Jewish Moses Mendelssohn was an accepted intellectual leader as early as the mid-18th century, but ordinary Jews did not attain full equality in Prussia until 1919, and then not for very long. Once both distortions are stripped away, the record of Prussian history uncovered by Mr. Clark is altogether more interesting, and surprising.

For example, one of the best remembered Prussian rulers is King Frederick William (Friedrich Wilhelm), famous all over Europe by the time he died in 1740 for his maniacal passion for uniforms, parades, and exceptionally tall soldiers, recruited all over Europe for their height alone, some of them victims of clinical gigantism and physically unfit for combat. Frederick William thus seems the perfect example of bird-brained militarism … except that he was exceedingly intelligent and a very creative administrator, personally responsible for the drastic reforms that created the Prussian state bureaucracy, whose rationality, honesty, and fiscal efficiency made it the envy of Europe. It was also guided by a Calvinist ruler who disliked spending. As a result, taxation was moderate as well as equitable — by will of the king, even the court paid luxury taxes.

Along the way, Frederick William invented the reserve conscription system still used by Switzerland and Israel, under which after their initial training, recruits go home to pursue their civilian lives but remain subject to an annual recall for refresher training and mobilization in wartime. Mostly landless laborers rather than farmers or craftsmen were called up, as well as the fit sons of the nobility, so that the damage to the economy was minimized. The overall result was that Prussia could prosper, while still fielding the fourth largest army in Europe, even though it ranked tenth in territory and thirteenth in population. Not that Frederick William made much use of his army — in a final contradiction, the militarist martinet was distinctly averse to war, leaving it to his effete, homophile, and brilliant son, who found drill unspeakably boring, to become Frederick the Great, by incessant and finally successful warfare.

Contradictions seem to mark every stage of Prussian history, including its end.

On February 25, 1947, the Allies — as they still were — promulgated in Berlin a law whose Article I was quite sufficient in itself: “The Prussian state together with its central government and all its agencies is abolished.” The reason was stated in the preamble, where the Prussian State was described as “a bearer of militarism and reaction,” and thus an impediment to the “reconstruction of the political life of Germany on a democratic basis” — that being the ostensible aim of the Allies in occupying Germany, even of Stalin’s Soviet Union, in words at least.

The allies need not have bothered. By then Prussia had ceased to exist. The German and protestant Slavic (Mazurian) populations of East and West Prussia, as well as of Lower and Upper Silesia, Posen, and most of Pomerania had been eliminated by flight, expulsion, deportation, individual murders, or Polish lynch mobs. The historic territory of East Prussia, originally conquered by the Teutonic knights from the Slavs, reverted to them after six centuries, for it was partitioned into the Soviet and now Russian Kaliningrad Oblast, including the old capital Königsberg of Kantian fame, Poland’s Warmian-Masurian Voivodeship, and Lithuania’s Klaipeda Region. Only Brandenburg, with its capital Berlin, the western slice of Pomerania, and a small part of Lower Silesia remained German, and even there the Prussian state structure did not have to be abolished, because the Nazis had already done it themselves.

Under the federal structure of the Weimar republic, the vast “Prussian free state” which stretched from the Rhine to Lithuania (except for the Polish corridor), enclosing both the Ruhr coal and steel centers and Berlin, with their large working-class populations, was consistently ruled by Social-Democratic governments under their outstanding leader, Otto Braun. It was there that the Nazis were resisted most effectively, and they did not win a majority within Prussia even in the last and heavily manipulated election of March 1933. Upon coming to power, Hitler reacted by appointing Hermann Göring as Prussian state police minister, before replacing all elected state governments with appointed governors two years later. It was the end of political Prussia. So the 1947 law was more exorcism than abolition.

As for the now forgotten Prussian reputation for religious tolerance, it was valid enough, but derived from necessity rather than liberality. The ruling Hohenzollern family had turned Calvinist at the beginning of the 17th century, but the vast majority of the population they ruled as Dukes, Electors, and Kings (from 1701) was Lutheran. Because Calvinism too has its variations, while Lutheranism has greater ones, including the pietist movement that shared in the Calvinist austerity, the doctrinal difference could have been overlooked to some degree. But the Calvinists could not abide the crucifixes and candles that Lutheran churches retained from their Catholic past, which they deemed evidence of lingering popery, and out of that difference — which all could see, unlike the doctrinal differences — there came riots, turmoil, and a dangerous fracture of loyalties.

The solution of Elector Johann Sigismund (1608–1619) was a fixed policy of religious tolerance, then unknown in Europe except in Holland, which came in handy when the cheerfully atheist Frederick the Great added Catholic lands to his kingdom. Under this dispensation, Judaism as a religion was also tolerated, though not necessarily the Jews, who were subject to many different municipal prohibitions and exclusions in as many municipalities and dependencies, not least because of the insistence of their local economic competitors in the merchant classes. Electors and Kings often objected in the name of enterprise and their tax base, but the centralization of the Prussian state that removed these local restrictions was a slow process. Only in their own capital of Berlin were the rulers of Prussia free to extend their hospitality to the better class of Jews, whose mansions were to house the leading intellectual and political salons of Berlin from the mid-18th century. Because they were the crucibles of Prussian reformist nationalism in reaction to Napoleon’s domination, that was one nationalism that was free of anti-Semitism, which was indeed scarcely compatible with the Calvinism and Lutheran pietism widespread in the Prussian elite.

Mr. Clark is very good on this subject but the same can be said of all his social history — including the entire phenomenon of the land-holding and variously aristocratic Junker class, with its own contradictions between feudal pretensions, a distinct scarcity of ready cash that forced them to manage their estates frugally, the resulting interest in salaried military service, and tendentially unwarlike pietism. Prussia was much more than its wars, but without its wars it would not have been Prussia, and they and their protagonists (Mr. Clark’s Bismarck is priceless), origins, conduct, and consequences occupy a large part of this excellent book, which scholars of Germany and Prussia will want to ponder very carefully, and which many an unencumbered reader will simply enjoy.

Mr. Luttwak last wrote for these pages about Islamic imperialism.