During World War I, Vilnius – as with the rest of Lithuania – was occupied by the German Empire from 1915 until 1918. The "Act of Independence of Lithuania", that restored Lithuanian independence from any affiliation to any other nation was proclaimed in the city on February 16 1918. After the withdrawal of German forces, Lithuanian forces were forced to retreat by advancing Russian occupation forces. Vilnius changed hands many times: for a while it was controlled by Polish self-defence units, who didn't want the city to be occupied by Russian-Bolshevik forces. Then the Polish Army regained control, then Soviet forces again. Shortly after its defeat in the Battle of Warsaw (1920), the retreating Red Army ceded the city back to Lithuania by signing a peace treaty on July 12, 1920. On October 9 of the same year, the Polish Army under General Lucjan Żeligowski broke the treaty and seized Vilnius after a staged coup. The city and its surroundings were proclaimed as the separate state of Central Lithuania. On February 20 1922 after an elections, the whole area was attached to Poland, with the city as the capital of the Wilno Voivodship (Wilno being the name of Vilnius in Polish). The predominant languages of the city were still Polish and, to a lesser extent, Yiddish.