His opposition to the SDAP joining coalition governments after it lost its leading position in Parliament in 1920 and his practice of advising the party to wait for the proper historical circumstances before taking action were criticized by some for facilitating Austria's move from democracy to fascism in the 1930s.

His political interests were reflected in his university studies, where in addition to law, history, languages and philosophy, he enrolled in classes in national economics and sociology.

At the university he met the somewhat older Socialist Party members Max Adler, Rudolf Hilferding (who later became a minister of finance in the Weimar Republic) and Karl Renner, who was Chancellor of Austria immediately after both the First and Second World Wars.

[5] In 1914 Bauer met and fell in love with Helene Landau [de] (née Gumplowicz), a married academic and journalist who was ten years his senior.

He took part as a platoon commander in the heavy fighting at Grodek (now Horodok, Ukraine), saved his company from being wiped out at the battle of Szysaki, for which he was awarded the Military Cross of Merit 3rd Class, and on 23 November 1914 was taken prisoner of war by the Russians during a "spirited" attack that he had ordered.

[8] As he wrote to fellow Social Democrat Karl Seitz, who sent him money through friends in Stockholm,[9] he was able to work on a comprehensive theoretical treatise during his imprisonment in Siberia.

[10] As a result of intervention by the SDAP, Bauer was able to return to Vienna as an exchange invalid in September 1917, less than two months before the outbreak of the October Revolution in Russia.

The SDAP's left wing had gained in importance at the party congress in 1917 because the plight of the civilian population that was going hungry due to wartime food shortages.

After Victor Adler's death on 11 November 1918, the 37-year-old Otto Bauer, seen as the young and dynamic leader of the SDAP's left wing, was brought into the party's leadership.

[14] He conducted confidential unification negotiations from 27 February to 2 March 1919 with German Foreign Minister Ulrich von Brockdorff-Rantzau, whose representatives in Austria warned internally against joining Germany with the small bankrupt state.

Bauer did not inform his government colleagues of the warning until weeks later[15] and initially nominated Franz Klein, who was known to be an ardent supporter of unification, as head of the delegation to the peace talks at St. Germain.

On 7 May 1919 the Allies of World War I handed the German delegation at Versailles the draft of the peace treaty, which revealed that the victors would not permit Austria to unite with Germany.

His successes were also due to the fact that in the course of the post-war economic boom that lasted for about two years, the revolutionary fervor of the working class had diminished considerably.

It was a period during which workers could find employment, earn a decent wage, pay hardly any rent, and in what had become known as "Red Vienna", were entitled to the first social benefits offered under its SDAP mayor Jakob Reumann.

One result of this was that Secretary of the Army Julius Deutsch had to relinquish control of the Austrian Armed Forces, which 14 years later was to play a decisive role in the suppression of social democracy.

[21] The program contained features from Marxism and the ideology of class conflict, and it provided the theoretical basis for political confrontation with the Christian Social Party and the paramilitary Heimwehr, which at the time were becoming increasingly clerical-fascist.

Bauer's revolutionary rhetoric, which used Marxist ideas to define the transition from capitalism to socialism as an inevitable historical necessity, largely overshadowed the party's concrete demands.

Bruno Kreisky, who was to become the Social Democratic Chancellor of Austria from 1970 to 1983, spoke of a terrible verbal mistake: "[The] phrase 'dictatorship of the proletariat' stuck to the party like a brand.

"[23] Bauer, with the approval of Seitz and Renner, rejected coalition offers by the Christian Socialist Chancellors Ignaz Seipel in 1931 and Engelbert Dollfuss in 1932.

"[24] On 4 March 1933 Bauer and Seitz sent party secretary Adolf Schärf to Karl Renner with the advice that he resign as first president of the National Council, due to what came to be known the rules of procedure crisis.

In early February 1934, Theodor Körner, who had been a general during World War I and was at the time Chairman of the Austrian Parliament's upper house, was asked at the last minute to take command of the Schutzbund.

The party's waiting was therefore to be seen as an appropriate "revolutionary pause", because any shared responsibility involving dubious partnerships (meaning coalition offers by the Christian Socialists) would only lead to delaying the collapse of the prevailing capitalist order.

Then the achievements of "Red Vienna", from which Bauer drew a good part of his strength and confidence, would serve not as the ultimate goal, but rather as the basis for further development toward a socialization of the economy that would be nearly impossible to reverse.

With his visions of the widespread upheavals that would inevitably follow an election victory, Bauer kept the left wing of the party in line for a long time, but after 5 March 1933 – the day the German Nazi Party won the largest share of seats in Germany's Reichstag election – the left wing accused him of inappropriate hesitation in defending against the advance of fascism.

The project, which was derided by Karl Radek, a Polish functionary of the Third International, as an "excretory product of the world revolution (decoctus historiae)", failed.

What was real had prevailed against material obstacles and human intentions, was accordingly an inevitable result of social development, necessary, and therefore as an evil at the same time good, for it was also the precondition of all better things to come.

The social philosopher Norbert Leser held that Bauer's death in 1938 prevented a difficult dispute over the post-war direction of the SPÖ: Had Otto Bauer – the brain and soul of Austromarxism – still been alive in 1945 and returned to Austria, it would hardly have been possible to avoid a dispute about the mistakes of the old leadership, but with him serving as a dead icon who was invoked on holidays but denied in everyday life, the postwar SPÖ got along fine.

In 1914 Otto Bauer rented an apartment in a middle-class building at the corner of Gumpendorfer Strasse 70 and Kasernengasse 2 in Vienna's 6th district of Mariahilf[35] and lived there until he fled Austria in 1934.

[37] Otto Bauer's son Martin, born in 1919, was a successful animator and film producer in Austria who was responsible for numerous remarkable television commercials in the 1950s and 1960s.

Otto's sister Ida Bauer (1882–1945) became known as a patient of Sigmund Freud, who wrote a famous case history about her in which he referred to her by the pseudonym "Dora".