In early 1942, the Communist Party of Yugoslavia (CPY) and the Alliance of Communist Youth of Yugoslavia (ACYY) formed a broad antifascist youth movement – the Alliance of the Young Generation as the forerunner of the Unified League of Antifascist Youth of Yugoslavia (ULAYY), which was established in November of that year. The majority of antifascist youth organizations in Yugoslavia joined ULAYY. The Unified League of the Antifascist Youth of Croatia (ULAYC) was active in Croatia as the republic body since its establishment in 1943. The ACYY and ULAYY played a vital role in the post-war period by implementing CPY policy, while actively conveying it at the same time.

The ACYY was a youth version of the CPY while ULAYY was established as a broader organization with the task of gathering all youth. In terms of structure, both organizations were copies of the CPY. Both the ACYY and the ULAYY acted under the auspices of the CPY as part of its programs and had little independence in decision-making. At its third congress in 1946, the ULAYY changed its name to the People’s Youth of Yugoslavia (PYY) and in 1948 the two youth organizations consolidated into a single organization, retaining the name PYY - in Croatia, People's Youth of Croatia.

In line with political changes at the state level and the adoption of new Constitutions, in 1963 the organisation changed its name to the Alliance of Youth of Yugoslavia/Croatia and in 1974 again, when it was finally named the Alliance of Socialist Youth of Yugoslavia / Croatia (ASYY / ASYC). For the duration of its existence, the ASYY/ASYC was a mass socio-political youth organisation that operated under the aegis of the League of Communists of Yugoslavia/Croatia.