July 14, 1889 was a historic date for more than one reason. Coming exactly a hundred years after the storming of the Bastille, this day was the central focus of the centenary of the French Revolution, marked by official state pageantry as well as the Left’s own celebrations. Yet socialists didn’t just commemorate the glorious events of a century before. Meeting in Paris on July 14–16, delegates of socialist parties from around the world declared a new international organization to cohere their efforts.

The Second International founded in 1889 followed in the wake of the earlier International Workingmen’s Association (1864–76), in which Karl Marx had played a leading role. Formed six years after his death, the new International united such parties as the German Social Democratic Party (SPD), the French socialists (SFIO), and Russia’s Social Democratic Labour Party (RSDLP). Mainly a European organization (with a smattering of delegates from the Americas and, later, Asia), it provided the key space for all development of socialist ideas and strategy in this period.

Today, the International is perhaps best known today for the circumstances of its collapse. Despite its longstanding campaign against militarism, in summer 1914 the International would splinter along national lines faced with the outbreak of World War I. This fiasco, and the denunciation of the Second International from Lenin onward, has however occluded more positive parts of its record, and its success in promoting the socialist project among millions of working people.