Social Democratic Union 'Proletarian' was a

political party A political party is an organization that coordinates candidates to compete in a particular country's elections. It is common for the members of a party to hold similar ideas about politics, and parties may promote specific political ideology ...

organization in

Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...

from 1906 until 1908. The organization was led by

Dimitar Blagoev Dimitar Blagoev Nikolov (, mk, Димитар Благоев Николов; 14 June 1856 – 7 May 1924) was a Bulgarian political leader and philosopher. He was the founder of the Bulgarian left-wing political movement and of the first social- ...

, who had been expelled from the

Narrow Socialists Bulgarian Social Democratic Workers' Party (Narrow Socialists) ( bg, Българска работническа социалдемократическа партия (тесни социалисти), translit=Balgarska rabotnicheska sotsialdemok ...

for being an "anarcho-liberal". 'Proletarian' merged with the

Broad Socialists The Bulgarian Social Democratic Workers Party (Broad Socialists) ( bg, Българска работническа социалдемократическа партия (широки социалисти), ''Balgarska rabotnicheska sotsialdemokra ...

, and would represent the left-wing tendency within that movement from 1909 onwards.Linden, Marcel van der, and Jürgen Rojahn.
The Formation of Labour Movements, 1870–1914: An International Perspective. Contributions to the history of labour and society, vol. 2
'.

Leiden Leiden (; in English and archaic Dutch also Leyden) is a city and municipality in the province of South Holland, Netherlands. The municipality of Leiden has a population of 119,713, but the city forms one densely connected agglomeration wit ...

: E.J. Brill, 1990. p. 406.

References

Defunct political parties in Bulgaria Social democratic parties in Bulgaria {{Bulgaria-party-stub