and Braunsberg (Braniewo). The city of Allenstein was separated from the Allenstein district in 1910 and became an independent city. In 1871, along with the rest of East Prussia, Warmia became part of the German Empire. In 1873, according to a regulation of the Imperial German government, school lessons at public schools inside Germany had to be held in German, as a result the Polish language was forbidden in all schools in Warmia, including Polish schools already founded in the sixteenth century. In 1900 Warmia's population was 240,000. In the jingoistic climate after World War I, Warmian Poles were subject to persecution by the German government. Polish children speaking their language were punished in schools and often had to wear signs with insulting names, such as "Pollack". After the First World War in the aftermath of the East Prussian plebiscite, carried when Red Army was marching on Warsaw - Polish–Soviet War in 1920, the region remained in Germany following a plebiscite in which 97% of residents voted in favor of remaining in Germany. Support for joining Poland was minimal even in Catholic Warmia, except for the Allenstein (Olsztyn) district where such support was quite high. Despite German hostility, the Poles founded numerous Polish organizations in Warmia in the interbellum. Persecution of Poles intensified after the Nazi Party rose to power in Germany. Due to severe persecution, from 1936 Polish organizations carried out their activities partly in conspiracy. Polish organizations were heavily invigilated by the Sicherheitspolizei (German security police) through its undercover agents, known as the Vertrauensmänner. Based on their information, the German police compiled files and lists of Poles who were supposed to be either executed or imprisoned in Nazi concentration camps. Nazi militants carried out attacks on Polish schools, organizations, printshops, shops. The persecution of Poles further intensified in 1939. In early 1939, many Polish activists were expelled. Afterwards, in an attempt to rig the results of an upcoming census and understate the number of Poles in the region, the Germans terrorized the Polish population, attacked Polish schools and organizations, and confiscated Polish pre-census information leaflets. In summer 1939 the German terror against the Poles even exceeded the terror from the period of the 1920 plebiscite. Poles were subjected to expulsions and arrests, there were terrorist attacks on Polish organizations and schools, Polish libraries were looted or destroyed, and entire volumes of Polish press were confiscated. In August 1939,