Active Struggle, a secret para-military organization. Shortly before the outbreak of the Great War he left the Revolutionary Faction and became a member of the internal opposition within the socialist movement. In August 1914 he joined the Polish Legions and served with distinction in the 1st Infantry Regiment of the 1st Brigade. Promoted to the rank of Lieutenant, in 1915 he was delegated to political service in the Central Powers'-occupied Congress Poland, where he was among the most active organizers of the secret Polish Military Organization (POW). After the Act of 5 November and the proclamation of the Kingdom of Poland as part of the Central Powers' plan of Mitteleuropa, Tomasz Arciszewski entered the city council of Warsaw. There he became the founder of trade unions and the editor of various socialist newspapers. After the collapse of Germany and Austria-Hungary at the end of World War I, on 7 November 1918 Arciszewski was appointed the minister of labour and social affairs in the Provisional Government of the Polish Republic led by Ignacy Daszyński. After Daszyński's government passed its responsibilities to Piłsudski and the consolidation of power in all parts of Poland occurred, Arciszewski was appointed the minister of postal services and telegraphic communication in the government of Jędrzej Moraczewski. He served at that post until 16 January 1919. Soon afterwards he was elected a member of the Sejm. During the Polish-Bolshevik War he organized various workers' voluntary units and supported the sabotage beneath Russian lines. After the war, in 1922 he was again elected member of the Sejm from the Socialist lists and held his post until 1935. One of the most prominent leaders of the socialists (between 1919 and 1939 he was the member of the Main Council of the PPS), Arciszewski gradually broke up with his former colleague Piłsudski, who abandoned the socialist ideas after Poland regained her independence. This made him one of the prominent leaders of the Centrolew coalition of centrist and leftist parties. Apart from his seat in the Sejm, between 1919 and 1934, and then from 1938 until the outbreak of World War II, Arciszewski was a member of the Warsaw's city council. Among other duties, he was also the founder of the Workers' Society of Friends of Children. After the outbreak of the Invasion of Poland of 1939, Arciszewski took part in the defense of Warsaw as one of the commanders of the