Ropp was expelled from Vilnius to Vitebsk. Interwar period Polish-Lithuanian conflict During World War I, Vilnius was occupied by Germany from 1915 until 1918. Still under German occupation, Council of Lithuania proclaimed the Act of Independence of Lithuania in Vilnius on 16 February 1918. Act proclaimed the restoration of the independent state of Lithuania with Vilnius as its capital. The German civilian administration of the Ober-Ost declined to pass full authority to Lithuania, which was not controlled by the Germans anymore. Instead, the Germans tried to control the area through promoting conflicts between local nationalities as it became clear that the German plan for the creation of Mitteleuropa, a net of satellite buffer states, failed. Finally, on 1 January 1919, the German garrison withdrew and passed the authority over the city to a local Polish committee, against the pleas of the Lithuanian administration. A Polish administration started to be formed. Former members of the local Polish Self-Defence formations, now formally part of the Polish Army, took over the posts while the Lithuanians withdrew along with the Germans. On 5 January 1919 the city was taken by Bolshevik forces advancing from the east. Vilnius was proclaimed the capital of the Lithuanian–Byelorussian Soviet Socialist Republic. For the next 4 months the city became a communist experiment in governance. During the course of that conflict, on 19 April 1919 the city was again seized by Poland (Vilna offensive), this time by forces of the regular Polish Army. A year later, on 14 July 1920, it was lost to Soviet forces again (this time, the Soviets were aided by Lithuanians, who were promised Vilnius). Shortly after the defeat in the Battle of Warsaw in 1920, the withdrawing Red Army handed the city over to Lithuania, following the Soviet–Lithuanian Peace Treaty of 12 July 1920. The treaty allowed for the transfer to Lithuanian authority of some part of the areas of the former Grand Duchy of Lithuania. Although the city itself, as well as its surroundings, were actually transferred, the fast pace of the Polish offensive prevented additional territories to be handed over by the Red Army and the disputed area was split into Lithuanian and Polish-controlled parts. Many historians argue that the main reason behind the Soviet agreement with Lithuania was to weaken Poland and hand the disputed territories to a weaker state, which Lithuania was at the time, to reconquer the area more