Vilnius to Lithuania. On 9 October 1920, the Polish Army surreptitiously, under General Lucjan Żeligowski, seized Vilnius during an operation known as Żeligowski's Mutiny. The city and its surroundings were designated as a separate state, called the Republic of Central Lithuania. Interwar Poland On 20 February 1922, after the highly contested election in Central Lithuania, the entire area was annexed by Poland, with the city becoming the capital of the Wilno Voivodeship (Wilno being the name of Vilnius in Polish). Kaunas then became the temporary capital of Lithuania. Lithuania vigorously contested the Polish annexation of Vilnius, and refused diplomatic relations with Poland. The predominant languages of the city were still Polish and, to a lesser extent, Yiddish. The Lithuanian-speaking population at the time was a small minority, at about 6% of the city's population according even to contemporary Lithuanian sources. The Council of Ambassadors and the international community (with the exception of Lithuania) recognized Polish sovereignty over Vilnius Region in 1923. Vilnius University was reopened in 1919 under the name of Stefan Batory University. By 1931, the city had 195,000 inhabitants, making it the fifth largest city in Poland with varied industries, such as Elektrit, a factory that produced radio receivers. World War II Nazi Germany had invited Lithuania to join the invasion of Poland and retake the historical capital Vilnius by force; however, President Antanas Smetona and most of the Lithuanian politicians declined this offer because they had doubts about Adolf Hitler's eventual victory and were outraged by the 1939 German ultimatum to Lithuania. Instead, they supported the neutrality policy and after being encouraged by the French and British diplomats – Lithuania adopted the Neutrality Act, which was supported by all the political forces. World War II began with the German invasion of Poland in September 1939. The secret protocols of the Molotov–Ribbentrop Pact had partitioned Lithuania and Poland into German and Soviet spheres of interest. On 19 September 1939, Vilnius was seized by the Soviet Union (which invaded Poland on 17 September). The Soviets repressed the local population and devastated the city, moving assets and factories to the USSR territory, including the major Polish radio factory Elektrit, along with a part of its labor force, to Minsk in Belarus SSR. The Soviets and Lithuania concluded a mutual assistance treaty on 10 October 1939, with which the Lithuanian government accepted the presence of Soviet military bases in various parts