This work by V. I. Lenin was written in 1915 and, as the title indicates, it focuses on the causes of the bankruptcy of the Second International. In 1914, when the First World War broke out, the leadership of the Second International sided with the bourgeoisie and betrayed the international proletariat.

Using dialectical materialism as a tool to analyze history, Lenin draws important conclusions about the nature of war and the stance of communists towards it. Criticizing the opportunist leaders of the Second International, he analyzes the causes of the emergence of opportunism within the workers' movement and characterizes it as a political appendage of the bourgeoisie within the workers' movement.

Through the ashes of the First World War, humanity entered a new historical phase. "The imperialist era is incompatible with the coexistence within the same party of the vanguards of the revolutionary proletariat and the semi-small-bourgeois aristocracy of the working class..."

In our time, an era of imperialist wars but primarily an era of transition from capitalism to socialism, studying this book helps us understand that the fight against opportunism must be continuous and uncompromising for communists.