The Ukrainian Social Democratic Labour Party (), also known as Esdeky and SDPists, was the leading party of the Ukrainian People's Republic. The party was reformed in 1905 at the Second Congress of the Revolutionary Ukrainian Party and was pursuing Marxism through the Social Democratic Party of Germany's Erfurt Program as well as national and cultural autonomy. Party leaders were Volodymyr Vynnychenko, Symon Petliura, Mykola Porsh, Dmytro Antonovych, Lev Yurkevych, Mykhailo Tkachenko, and Mykola Kovalsky.
The party identified its priority by resolving national matter and pushing its struggle for social liberalization of working class to the secondary set. In the spring of 1905, in his polemics with Dmytro Antonovych that was covered on pages of the party publishing Pratsia, Mykola Porsh argued his opinion about dependence of social and economic oppression from national. He insisted that for overcoming the social oppression foremost is necessary to solve the national issue. In Soviet propaganda, the party was identified as a petty bourgeoisie nationalistic party that was renamed as Ukrainian Social Democratic Labour Party to deceive people. Vladimir Lenin characterized the party as "representatives of the most low-grade, stupid and reactionary nationalism" who betray "interest not only democracy in general, but its own fatherland, Ukraine."
History
With the ongoing Revolution of 1905 the party was reformed based on already existing Revolutionary Ukrainian Party (RUP) based from Kharkiv in December 1905 at the 2nd Party Congress of RUP. The party adopted the Erfurt Program of Social Democratic Party of Germany.
In December 1905, the Ukrainian Social-Democratic Labour Party (USLDP) decided to join the Russian Social Democratic Labour Party, provided it was recognised as the sole representative of the Ukrainian proletariat, within the RSDLP. The Fourth (Unity) Congress of the RSDLP rejected the proposal which the USDLP spokesman had made for the immediate discussion of the terms of a merger, and referred the matter to the Central Committee for decision. At the USDLP party congress in June 1907 the party adopted its resolution that was similar to ultimatum urging RSDLP to recognize Ukrainian autonomy, Ukrainian Social-Democracy must have its representative in the Central Committee of RSDLP, and accept USDLP as the RSDLP's national organization of Ukrainian proletariat. No agreement was reached on a merger. Arguably, the reason that there was no merger was the fact that the USLDP, the UPSR, and the URLDP all favoured an independent Ukrainian state.
After the USDLP party congress in March 1907 its activity were semi-active. The party also closely worked with the Jewish Bund subsequently including the Ukrainian Jewish into the government of Ukraine; as well as other menshevik factions which altogether accounted for around 3,000 members. In 1908 the USDLP was suspended and many of its activist went into exile, particularly to the Austrian Galicia (today Western Ukraine). In 1915 in Ukraine was revived the party's central committee bureau in place of its regular central committee. In 1914 just before the World War I, a group of USDLP activist who went into exile and led by Dmytro Dontsov and Volodymyr Doroshenko joined the Galician social democrats, national democrats and radical to form the Union for the Liberation of Ukraine. The "Union" declared its loyalty to the Central Powers (Austria-Hungary and German Empire) considering that they could help Ukraine to free from the Russian domination. Another group on contrary supported the Tsarist Russia. Such position was held by an editor of published in Moscow newspaper Ukrainskaya zhyzn (Ukrainian life) Symon Petlyura and his supporters. The rest of members took an anti-war internationalist position. Such position of proletarian internationalism had been held by the USDLP abroad organization publishing in Geneva, newspaper Borotba (Fight).