Social Democratic Labor Party (Bolshevik) (RSDLP(b)). In 1917, he became the editor of Lithuanian socialist (later communist) newspaper Tiesa. In August 1917, he participated in the 6th congress of RSDLP(b) in Petrograd and supported the creation of the Communist International (Comintern). After the 1917 Russian October Revolution, Mickevičius served as the Commissar of the Soviet government for Lithuanian affairs and was a member of the Central Bureau of the Lithuanian Sections under the Central Committee of the RSDLP(b) and then of the Russian Communist Party (Bolsheviks) (RCP(b)). In late 1918, Mickevičius returned to Lithuania (then still occupied by Germany; see Ober Ost) to head the socialist revolution there. Lithuania was contested by many forces: the German occupation was still in place, the Council of Lithuania proclaimed independence on 16 February 1918, the Polish government was in favor of a Polish–Lithuanian federation (in the spirit of the former Polish–Lithuanian Commonwealth). The socialist forces (LSDP, social democratic labor party, Jewish Bund, social democrats-revolutionaries etc.) were actively organizing in Vilnius and other Lithuanian towns. In early October, the founding congress of the Lithuanian Communist Party took place in Vilnius. In December, elections were held for the Vilnius Soviet of Workers' Deputies electing 96 communists and their non-affiliated sympathizers, 60 Bund members, 22 Mensheviks and 15 LSDP members (social democrats). On 8 December 1918 the Vilnius Soviet formed the Provisional Revolutionary Workers' and Peasants' Government of Lithuania. Mickevičius was elected the Chairman of the new government (Prime Minister) and the Minister of Foreign Affairs. On 16 December 1918 the Mickevičius government issued a manifesto, in which they dismissed German occupational administration and proclaimed the Lithuanian Soviet Socialist Republic. German occupying forces were still stationed in Vilnius but started leaving in late December 1918, while the Red Army moved westward trying to regain lands given up by the Brest-Litovsk Treaty. On 2 January 1919 the Polish Committee forces (Samoobrona) took control over Vilnius. The Council of Lithuania withdrew to Kaunas the same day. The Red Army entered Vilnius on 5 January and the Mickevičius government reestablished its control. On 27 February 1919 the Lithuanian SSR and Belarusian SSR were merged and the Lithuanian–Belorussian Soviet Socialist Republic (Litbel) was formed. Mickevičius served as the Chairman and Minister of Foreign Affairs of the Litbel government. Polish military offensive of 1919 against the Red Army was pushing into the territory of Litbel, while newly established Lithuanian Army was