The Sammarinese Democratic Union was a conservative political movement in San Marino and a counterpart of the liberal coalition which ruled Italy before the fascist era.
Even if the country was officially neutral, many volunteers supported the Italian struggle alongside the democratic world, and the inflation striking the Italian lira hugely touched the Sammarinese economy, and finally the social and political life.
Strikes and violence exacerbated the political situation, with the landowners taking strength in a match of respective extremisms.
Despite the Union's third-place finish in the now-proportional elections of 1920 behind the centrist Sammarinese People's Party and the Socialists, it began to be heavily helped by its Italian counterpart and, later, directly by some Fascist squads led by Italo Balbo, and by a Carabinieri garrison called by the Sammaninese government after the murder of Fascist activist Bosi on May 21, 1921.
The Socialists were banned from the elections of 1923, during which the Union joined the Fascist-led Patriotic Bloc with all other centre-right forces.