Rio Palace Hotel. The Congress brought together 77 participants from 50 countries, under the chairmanship of former West German Chancellor Willy Brandt. The Socialist International (SI) is an international organization that seeks to disseminate and implement democratic Socialism through the union of social democratic political, socialist and labor parties. It was founded in 1951 under the name Labour and Socialist International, and it currently has 160 party members in over 100 countries around the globe, one of the largest party organizations in activity.