The growth of socialist parties after 1871 was phenomenal. By 1912, Germany’s Social Democratic Party had millions of followers — mostly people from the working classes — and was the largest party in the Reichstag. Socialist parties grew in other countries as well, though nowhere else with such success.

Marxist socialist parties were eventually linked together in an international organization: the International Working Men’s Association. Marx himself played an important role in founding the group, also known as the First International. In the following years, he battled successfully to control the organization and used its annual meetings as a means of spreading his doctrines. Marx enthusiastically endorsed the radical patriotism of the Paris Commune and its terrible struggle against the French state as a giant step toward socialist revolution. Marx’s embrace of working-class violence frightened many of his early supporters, especially the more moderate British labor leaders. The First International collapsed.

Yet international proletarian solidarity remained an important objective for Marxists. In 1889, as the individual parties in different countries grew stronger, socialist leaders came together to form the Second International, which lasted until 1914. The International had a permanent executive, and every three years delegates from the different parties met to interpret Marxist doctrines and plan coordinated action. May 1 (May Day) was declared an annual international one-day strike, a day of marches and demonstrations.