The Second International, also known as the Socialist International, is an international alliance of socialist parties and workers 'groups from various countries.

On July 14, 1889, the Congress of Socialists in Paris, attended by 393 delegates from 22 countries, announced the birth of the Second International. The Second International was a loose alliance that took 11 years to establish its executive body, the Executive Board of the International Socialist Party, with its headquarters in Brussels. In the early days, under the guidance of Siggs, the active struggle against anarchism, the dissemination of Marxism, and the development of the working-class movement in various countries achieved significant results. At that time, capitalism was in a period of relatively peaceful development, and the trend of right-wing opportunism was growing in the Second International.

After Engels's death in 1895, this trend of thought took the lead of the Second International, falsifying and attacking Marxism, promoting bourgeois reformism, and degenerating the Second International. During the First World War, with the exception of Serbia and the Russian Bolshevik Party represented by Lenin, all other socialist parties supported their own bourgeois governments, supported imperialist wars, and degenerated the Second International into social chauvinism.