In the early 1920s, a group of young militants of the Social Democratic Party (Alþýðuflokkur) came into contact with the international communist movement.
The group evolved into the "Sparta Association of Socialists" (Jafnaðarmannafélagið Sparta) in 1926, but they eventually left the social democrats to form their own party as suggested by Comintern in 1928.
The Communist Party of Iceland (KFI) was formed in November 1930 and became a member of Comintern.
In 1938, another splinter group, which had left the social democrats the year before, unified itself with the communists forming the Popular Unity Party - Socialist Party (Sameiningarflokkur alþýðu - Sósíalistaflokkurinn).
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