When Adolf Hitler left provincial Linz in late adolescence there was only one place to go: Habsburg Vienna, the great imperial city. But the crowded streets of Vienna through which he wandered as a destitute young artist were dark with shadows of change and threat.

Hitler arrived in Vienna in 1907, leaving for Munich in 1913, a period when the Austro-Hungarian empire was unravelling, its disparate peoples inflamed by incipient nationalism. Everyone, it seemed, was in revolt against the long-nurtured assimilationist, multinational ideals of Franz Joseph, emperor of Austria since 1848 and king of Hungary since 1867. The romantic nationalism of the pan-Germans, in particular, led by Georg von Schonerer, had drawn support. Dr Karl Lueger, the mayor of Vienna, was using his considerable gifts as an orator to scourge Slav emigration and Jews. The Zionist movement, recently founded, was vocal and committed. The Balkans, meanwhile, gently seethed, like a geyser waiting to erupt.

Political turmoil was paralleled by a different kind of turmoil in the arts. Artistic-intellectual fin-de-siecle Vienna was a world of radical innovation- the world of Freud, Mahler, Wittgenstein, Klimt, Schoenberg and the architect Adolf Loos. But this wasn’t Hitler’s Vienna, as Brigitte Hamann shows in her superb new study. Rather, Hitler’s Vienna was a city of the “little” people, insurgent on all fronts, a city of the disadvantaged, of the hungry and homeless, of poverty, isolation and threat. The people among whom Hitler mingled were unsettled by Viennese modernity. They viewed the new modernist cultural order as “degenerate”, too cosmopolitan and libertine, too “Jewish”- a dire symptom of fragmentation and decay.

Degeneracy was everywhere apparent in Hitler’s Vienna, its manifestation identified in anything from the emancipation of women to expressions of Jewish self-hatred. “We are now fully infected by serious popular mental illness, a sort of black plague for degeneration and hysteria,” wrote Max Nordau, a German-speaking Jew from Hungary. “The degenerates babble and stammer instead of talking…They draw and paint like children who with useless hands dirty tables and walls. They make music like the yellow people in East Asia. They mix together all artistic genres.”

George Steiner, reviewing the German edition of Hamann’s book last year, likened the young Hitler to the narrator of Knut Hamsun’s great debut novel Hunger (1889). The comparison is instructive. The young Hitler, like Hamsun’s narrator, was morbidly introspective and isolated, although utterly convinced of his talent. Like the narrator, Hitler came from the provinces to wander the streets of the metropolis in search of high culture, a lonely, ostracised figure, a fanatic of perpetual indignation for whom social intercourse was a tiresome impossibility. His friend Gustl Kubizek, with whom he shared a room in 1908, recalled how Hitler would bully him with speech. Hitler, like the narrator, was a failed artist, an aspirant painter and architect who was rejected by the Academy for Visual Arts, the summit of all his youthful ambitions.

Having been rejected from the academy, Hitler wrote in Mein Kampf: “Downcast, I left von Hamsun’s magnificent building on the Schillerplatz [the academy building], for the first time in my young life at odds with myself.” He knew then that if he was to progress it would be as an “auto-didact”. And so began his restless years of street wandering, of buying cheap tickets for the opera (he was obsessed with Wagner), watching the debates in parliament, where politicians addressed one another in a Babel of languages, studying architecture, writing into the night and sleeping late, consumed by a will to greatness.

At this stage, he lived in cheap accommodation, in shelters, bedsits and hostels, mingling with the outcast of the city. He cultivated the role of neurotic outsider and his sustenance was a kind of wounded contempt, as he grappled with what he called his “struggle for survival in Vienna” and his “constant unappeasable hunger”.

What prevented Hitler from progressing as an artist was not his lowly status, nor any kind of establishment conspiracy, but a fundamental lack of talent. His drawings - hurriedly produced and sold so that he might eat - were at best mediocre, as he himself acknowledged when, as Fuhrer, they were being valued at outlandish prices. And yet, Hitler had talent, a diabolical, world-transforming talent: a talent to exploit, organise and inflame mass man.

With discipline and diligence to primary sources, Hamann shows how he came first to accommodate himself with, and then to harness, his talent; she offers a portrait of real complexity, of a young man for whom life was perceived as a kind of mystical quest, a quest for supreme self, assertion that found its ultimate expression in a messianic pan-German nationalism that flowed like an ocean into the spaces left behind by the disintegrating Habsburg empire.

Hamann works hard to dispel many of the false assumptions regarding Hitler’s youth: that he had Jewish antecedents; that he was an anti-Semite from the moment he arrived in Vienna (he had several Jewish friends); that he abandoned his mother as she lay dying alone at the age of 46 (in fact, he was a caring son and returned from Vienna to nurse his mother, whose doctor said that he had never seen anyone “as prostrate with grief as Adolf Hitler”); that Jewish academics played apart in his rejection from art school.

Nazism, although utterly a product of the time, was an extraordinarily flexible, inclusive, DIY, perhaps uniquely Austrian ideology. By recreating the atmosphere of the last days of imperial Vienna, Hamann shows how Hitler became a kind of ideological kleptomaniac, stealing ideas from the pan-Germans, Teutonic supremacists and the Schonerians, from Nordic myths and old Germanic history, from folkish race theoreticians such as Guido von List and the English-born Houston Stewart Chamberlain (with their ideas of Aryan supremacy) and misappropriating Otto Weininger, Nietzsche and assorted others. But without the Great War, she argues, without Hitler’s experiences of the trenches and the subsequent humiliation of Versailles, he would never have been galvanised into apocalyptic rebellion.

Hamann shows that Hitler’s one trick of evil brilliance - his essential difference from other pan-German fanatics such as yon Schonerer - was not to have numerous enemies but one central, unifying enemy: the Jews, the diabolical Other on to whom the agitated “little” people could project their deepest fears and loathing. She seldom slips into a tone of condemnatory didacticism; like a good reporter, she shows, but never prescribes. And she understands, too, that Hitler’s Vienna, that her Vienna, which she animates so vividly in its multi-ethnic diversity, will for ever more be a Vienna of the imagination, a make-believe city whose teeming streets are clamorously alive with the rough collision of Magyars, Croats, Slovenes, Slovaks, gypsies, Romanians, Poles, Italians, Germans, Czechs, Ruthenians and, above all, with Jews. It’s all long gone now.