Alexandre Millerand in the context of "San Remo conference"

The Socialist International, commonly known as the Second International, was a political international of socialist and labour parties formed in Paris on 14 July 1889. At a time of growing industrial working-class movements and the expansion of suffrage, it brought together autonomous national parties into a loose international federation. It continued the work of the First International (1864–1876), from which it inherited both the legacy of Karl Marx and the conflict with anarchists. The organization was dominated by the powerful Social Democratic Party of Germany (SPD), whose organizational and theoretical leadership heavily influenced the other member parties.

The International established the annual celebration of International Workers' Day on 1 May and popularised the demand for an eight-hour day. Its early congresses were preoccupied with expelling anarchists and defining its mission as one based on parliamentary political action. After 1900, the International was increasingly confronted with the internal divisions of the socialist movement, particularly the rise of revisionism in Germany and the debate over socialist participation in "bourgeois" governments, sparked by the Millerand affair in France. The 1904 Amsterdam Congress, which saw a major debate between French socialist Jean Jaurès and German leader August Bebel, condemned revisionism and ministerialism, marking the highest point in the influence of the International.