Albin Ström was a leftwing Social Democrat from Gothenburg who led a split from the Social Democratic Party in 1934, taking with him a few thousand members from the West Coast region.
The tendency of Ström founded the daily Arbetarposten (Workers' Mail) and quickly aligned itself with Karl Kilbom and Nils Flyg's splinter Communist Party (not aligned to Moscow).
When SP, under the leadership of Nils Flyg, gradually orientated itself towards Nazism, many of its members left the party.
The tendency of Ström broke away in 1940 and formed Vänstersocialistiska Partiet, after that Flyg had promoted that the SKP were to be suppressed by the state.
In 1945, a group of VSP militants, including Evald Höglund (who later formed the trotskyist RSP) and Anton Nilson, left the party due to their perception of the party taking a pro-Western Bloc position.