Complex sentence: From October 1863 to August 1864 he was Dictator of Insurrection, since October 17,1863 to April 20,1864 he was a head of Polish National Government, and president of its Foreign Affairs Office.
Split into simpler sentences: From October 1863 to August 1864 he was Dictator of Insurrection. He headed the Polish national government from October 17,1863 to April 20,1864, and was president of its Foreign Affairs Office.