Friedrich Engels was a German philosopher, political theorist, historian, journalist, and revolutionary socialist. He was also a businessman and Karl Marx's closest friend and collaborator.

The Second International (1889–1916) was an organisation of socialist and labour parties, formed on 14 July 1889 at two simultaneous Paris meetings in which delegations from twenty countries participated. The Second International continued the work of the dissolved First International, though excluding the powerful anarcho-syndicalist movement. While the international had initially declared its opposition to all warfare between European powers, most of the major European parties ultimately chose to support their respective states in World War I. After splitting into pro-Allied, pro-Central Powers, and antimilitarist factions, the international ceased to function. After the war, the remaining factions of the international went on to found the Labour and Socialist International, the International Working Union of Socialist Parties, and the Communist International.