Bolded the meaty bits for the TL;DRers:
With the victory of the Russian Revolution, and the collapse of the Hohenzollern and Habsburg empires in central Europe, key theorists of German communism came to believe that, in the aftermath of the First World War, the seizure of power by the proletariat was on the immediate agenda in every imperialist country, because the world had now definitively entered the historical epoch of the socialist revolution. This belief was most fully and forcefully expressed by Georg Lukács, then a leading member of the exiled Hungarian Communist Party, writing in the German-language theoretical review Kommunismus in Vienna. For Lukács, there was now a 'universal actuality of the proletarian revolution', determined by the general stage of the development of capitalism, which was henceforward in mortal crisis. 'This means that the actuality of the revolution is no longer only a world- historical horizon arching over the self-liberating working class, but that revolution is already on its agenda . . . The actuality of the revolution provides the key-note of the whole epoch.' This fusion — confusion — between the theoretical concepts of historical epoch and historical conjuncture allowed Lukács and prominent colleagues in the KPD such as Thalheimer and Frohlich to ignore the whole problem of the concrete preconditions for a revolutionary situation by abstractly affirming the revolutionary character of the time itself. On this premise, they went on to argue for a novel practical tactic: the Teilaktion or 'partial' armed action against the capitalist State.
Within the ranks of the Second International, Bernstein and co-thinkers had maintained the possibility of 'partial' ameliorations of capitalism by means of parliamentary reforms, that would in a gradual process of evolution eventually lead to the peaceful completion of socialism. The illusion that the inherent unity of the capitalist State could be divided or attained by successive partial measures, slowly transforming its class character, had been a traditional prerogative of reformism. There now, however, emerged an adventurist version of the same fundamental error in the Third International. For in 1920-21, Thalheimer, Frohlich, Lukács and others theorized putschist 'partial actions' as a series of armed attacks against the bourgeois State, limited in scope yet constant in tempo. In the words of Kommunismus: 'The principal characteristic of the present period of the revolution lies in this, that we are now compelled to conduct even partial battles, including economic ones, with the instrumentalities of the final battle', above all 'armed insurrection'. There was thus created the famous theory of the 'revolutionary offensive'.Since the epoch was revolutionary, the only correct strategy was an offensive one, to be mounted in a series of repeated armed blows against the capitalist State. These should be undertaken even if the working class was not in an immediately revolutionary mood: they would then precisely serve to 'awaken' the proletariat from its reformist torpor. Lukács provided the most sophisticated justification of these adventures. He argued that partial actions were not so much 'organizational measures by which the Communist Party could seize State power' as 'autonomous and active initiatives of the KPD to overcome the ideological crisis and menshevik lethargy of the proletariat, and standstill of revolutionary development'. For Lukács, the rationale of the Teilaktionen was thus not their objective aims, but their subjective impact on the consciousness of the working class. 'If revolutionary development is not to run the risk of stagnation, another outcome must be found: the action of the KPD in an offensive. An offensive signifies: the independent action of the party at the right moment with the right slogan, to awaken the proletarian masses from their inertia, to wrest them away from their menshevik leadership by action (in other words organizationally and not merely ideologically), and thereby to cut the knot of the ideological crisis of the proletariat with the sword of the deed.'
The fate of these pronouncements was rapidly settled by the lesson of events themselves. The radical misunderstanding of the integral unity of capitalist State power, and the necessarily all-or-nothing character of any insurrection against it, naturally led to disaster in Central Germany. In March 1921, the KPD launched its much vaunted offensive against the Prussian State government, by falling into the trap of a badly prepared rising against a preventive police occupation of the Mansfeld-Merseburg area. In the absence of any spontaneous working-class resistance, the KPD desperately resorted to dynamiting actions designed to prove police bombardments; seizure of factories and street fighting followed; wandering guerrilla bands submerged any discipline in anarchic forays through the countryside. For a week, heavy fighting raged in Central Germany between KPD militants and the police and Reichswehr units mobilized to suppress them. The result was a foregone conclusion. Isolated from the rest of the German proletariat, bewildered and dislocated by the arbitrary character of the action, hopelessly outnumbered by the concentration of Reichswehr troops in the Merseburg-Halle region, the vanguard flung into this confrontation with the full might of the army was routed. A drastic wave of repression succeeded the March action. Some 4,000 militants were sentenced to prison, and the KPD received its quietus in Prussian Saxony. Not only was the objective of State power never achieved, but the subjective impact on the German working class and the KPD itself was calamitous. Far from rousing the proletariat from its 'menshevik lethargy', the March Action demoralized and disillusioned it. The vanguard zone of the Merseburg mines relapsed into a desert of apolitical backwardness.
Helpfully, Anderson provides some contemporary criticisms of Teilaktionen by some people who knew something about successful revolutions.
A purely mechanical conception of the proletarian revolution — which proceeds solely from the fact that the capitalist economy continues to decay — has led certain groups of comrades to construe theories which are false to the core: the false theory of an initiating minority which by its heroism shatters 'the wall of universal passivity' among the proletariat, the false theory of uninterrupted offensives conducted by the proletarian vanguard as a 'new method' of struggle, the false theory of partial battles which are waged by applying the methods of armed insurrection and so on. … It is absolutely self-evident that tactical theories of this sort have nothing in common with Marxism. To apply them in practice is to play directly into the hands of the bourgeoisie's military-political leaders and their strategy.
And Lenin, a bit more tersely:
…for victory and for retaining power, what is essential is not only the majority of the working class — I use the term working class in its West European sense, i.e. in the sense of the industrial proletariat — but also the majority of the working and exploited population. Have you thought about this?