The historiography of World War I is immense, more than 25,000 volumes and articles even before next year’s centenary. Still, Clark, and Sean McMeekin, in “July 1914,” offer new perspectives. The distinctive achievement of “The Sleepwalkers” is Clark’s single-volume survey of European history leading up to the war. That may sound dull. Quite the contrary. It is as if a light had been turned on a half-darkened stage of shadowy characters cursing among themselves without reason. He raises the curtain at 2 a.m. on June 11, 1903, 11 years before Sarajevo. We see 28 Serbian army officers shoot their way into the royal palace in Belgrade. King Alexandar and Queen Draga, betrayed and defenseless, huddle in a tiny closet where the maid irons the queen’s clothes. They are butchered, riddled with bullets, stabbed with a bayonet, hacked with an ax and partially disemboweled, their ­faces mutilated beyond recognition and the bloody half-naked remnants tossed from the royal balcony onto the grounds.

Clark argues a direct connection between the assassins of Belgrade and Sarajevo. Though the regicide — and the murder of a repressive prime minister the same night — led to a more genuine parliamentary democracy, the conspiratorial network remained, its murderous passions now directed to undermining Austria-Hungary. The chief instigator of the Belgrade plot, Lieut. Dragutin Dimitrijevic, called Apis for his bull-like physique, became the head of Serbian military intelligence and was instrumental in the creation of the Black Hand terrorist networks that organized the assassination of the archduke. They dreamed of a greater Serbia encompassing all the Serbs on the Balkan Peninsula. The region was fertile ground for disaffection: two non-Slavic races, Austrians and Hungarians, held sway over millions of Serbs, Slovaks, Czechs, Croats and Poles, among others.

Clark gives us a thoroughly comprehensible and highly readable account of the polarization of the continent. It is a pity that with so many characters and so many unfamiliar names, his editors fail to provide a list of the players and chronology: one has to go to McMeekin for that.

An American professor who teaches in Istanbul, McMeekin has chosen the zoom lens. He opens with a crisp but vivid reconstruction of the double murder in the sunshine of Sarajevo, then concentrates entirely on unraveling the choreography day by day, as the hereditary monarchs in their palaces summon their ministers and generals and the ministers summon their aides for the writing and encryption of telegrams, and the ambassadors in top hats and tails in Vienna and Berlin, Belgrade and St. Petersburg, Paris and London summon all their eloquence and guile to follow up with their own glosses on their masters’ flow of threats, ­promises and entreaties. The imperial monarchs were ­related — Queen Victoria died in the arms of her grandson, Kaiser Wilhelm II — but they were also consumed by great- power rivalries and their individual authority was refracted through receding mirrors of bureaucracy. We get an indication of the ambiguities at a crucial point on the evening of July 29. Czar Nicholas II, having just agreed to general mobilization, is handed a telegram, appealing to him not to do just that. It is to “Nicky” from his third cousin in Berlin, Kaiser “Will.” Nicky instantly rescinds the order: “I will not become responsible for a monstrous slaughter.” Less than 24 hours later, kinship and prudence succumb to patriotic rhetoric and inflated estimates of Austrian military power.

Both authors put a stake through the heart of a common narrative that has Germany mobilizing first so as to spring the preventive war its generals had long advocated. It didn’t. Clark documents how Berlin’s political and military leaders stuck to their blithe belief that any conflict could be localized. Russia’s ­mobilization, he says, was “one of the most momentous decisions of the July crisis. This was the first of the general mobilizations.” McMeekin says that Russia’s crime was first in escalating a local quarrel by encouraging Serbia to stand up to Austria-Hungary and then accelerating the rush to war. He faults Barbara Tuchman in her classic “Guns of August” for misdating Russia’s mobilization two days later than it was ordered. He is no apologist for Germany. In “The Berlin-­Baghdad Express” (2010), he nailed the Kaiser as a half-crazy jihadist inciting Muslims against Anglo-French interests in the faltering Ottoman Empire, but his 2011 book “The Russian Origins of the First World War” lived up to its title.

Clark lends authority by citing Russian-French falsifications of documents. The Russians backdated and reworded papers in the records. The French were even more inventive, fabricating a telegram reporting six days of war preparations by Germany that weren’t happening. In Clark’s phrase, both Russia and France were at pains, then and later, to make Berlin appear “the moral fulcrum of the crisis.”

McMeekin is intent on indicting the men and nations he considers guilty. He could have entitled his book “J’accuse.” It’s his third with a polemical thrust. Clark declines to join McMeekin in what he calls “the blame game,” because there were so many participants. He argues that trying to fix guilt on one leader or nation assumes that there must be a guilty party and this, he maintains, distorts the history into a prosecutorial narrative that misses the essentially multilateral nature of the exchanges, while underplaying the ethnic and nationalistic ferment of a region. “The outbreak of war in 1914,” he writes, “is not an Agatha Christie drama at the end of which we will discover the culprit standing over a corpse in the conservatory with a smoking pistol.” Not having a villain to boo is emotionally less satisfying, but Clark makes a cogent case for the war as a tragedy, not a crime: in his telling there is a smoking pistol in the hands of every major character.

Still, his objectivity does not equate with a bland neutrality. By a stringent line-by-line analysis of the terms of Austria’s 48-hour ultimatum to Serbia and the Serbian reply, Clark demolishes the standard view that Austria was too harsh and that Serbia humbly complied. Austria demanded action against irredentist networks in Serbia. It would have been an infringement of sovereignty, yes, but Serbian tolerance of the terrorist networks, and its laid-back response to the Sarajevo murders, inhibit one’s sympathy with its position. Clark describes Austria’s ultimatum as “a great deal milder” than the ultimatum presented by NATO to Serbia-Yugoslavia in the March 1999 Rambouillet Agreement for unimpeded access to its land. As for Serbia’s reply, so long regarded as conciliatory, Clark shows that on most policy points it was a highly perfumed rejection offering Austria amazingly little — a “masterpiece of diplomatic equivocation.”

In sketching the characters of the key players, Clark makes a fascinating point I’ve not seen before: not simply were all the political players in the drama male, but they were men caught in a “crisis of masculinity.” He cites historians of gender who argue that at this particular time “competition from subordinate and marginalized masculinities — proletarian and nonwhite for example” accentuated assertiveness. You’d expect the military men to exude testosterone, and they do, but Clark is struck by how ubiquitous in memoir and memorandums are pointedly masculine modes of comportment, and how closely they are interwoven with their understanding of policy. “Uprightness,” “backs very stiff,” “firmness of will,” “self-castration” are typical modes of expression.