Founded in 1907 at the Congress of Stuttgart, the first International of Socialist Youths was rebuilt at the Congress of Hamburg in 1923 after the impact of the Bolshevik revolution and the great divides which followed. Areas of reflection and action for the ISY were primarily the protection of youth, education, propaganda and solidarity. In July 1929, the ISY had a spectacular demonstration of its strength as it brought together more than 200 000 members for its Congress of “red Vienna”. Here the young Socialists marched en masse shouting « never another war! ». The rejection of fascism and war provided a very firm basis for solidarity. But there were also strongly-felt differences, if not outright dissensions, between the more revolutionary (minority) Latin federations and the more reformist Scandinavian federations, who recovered the ISY leadership after the forced withdrawal of the Germans. However, unity was clearly the order of the day, as demonstrated by the last Lille Congress in July 1939. At this congress, the slogan “socialism means peace !” became most meaningful.