During the interwar period of the 20th century (1920–1939), Lithuanian–Polish relations were characterized by mutual enmity. As a consequence of the conflict over the city of Vilnius, and the Polish–Lithuanian War, both governments – in the era of nationalism which was sweeping through Europe – treated their respective minorities harshly. In 1920, after the staged mutiny of Lucjan Żeligowski, Lithuanian cultural activities in Polish controlled territories were limited and the closure of Lithuanian newspapers and the arrest of their editors occurred. One of them – Mykolas Biržiška was accused of state treason and sentenced to the death penalty and only the direct intervention by the League of Nations saved him from being executed. He was one of 32 Lithuanian and Belarusian cultural activists formally expelled from Vilnius on 20 September 1922 and deported to Lithuania. In 1927, as tensions between Lithuania and Poland increased, 48 additional Lithuanian schools were closed and another 11 Lithuanian activists were deported. Following Piłsudski's death in 1935, the Lithuanian minority in Poland again became an object of Polonization policies with greater intensity. 266 Lithuanian schools were closed after 1936 and almost all Lithuanian organizations were banned. Further Polonization ensued as the government encouraged settlement of Polish army veterans in the disputed regions. About 400 Lithuanian reading rooms and libraries were closed in Poland between 1936 and 1938. Following the 1938 Polish ultimatum to Lithuania, Lithuania re-established diplomatic relations with Poland and efforts to Polonize Lithuanians living in Poland decreased somewhat.