Germany’s defeat in 1918 had especially dire consequences for the province. It was cut off from the rest of the Reich by the so-called "Polish Corridor". Economic crisis, unemployment and hyperinflation in the 1920s had especially severe effects on East Prussia because of its geographic isolation and did nothing to strengthen faith in the new form of government.
The Versailles Peace Treaty came into force in 1920. In Germany, peace was seen as humiliating dictated peace and especially because of the cessions of territory in particular, it was violently rejected by all parties.
West Prussia fell in large parts to the resurrected Poland, in East Prussia this concerned the area around Soldau (today Działdowo) near Neidenburg (today Nidzica). In the north, the Memel territory was cut off and put under the supervision of the League of Nations, then annexed by Lithuania in 1923.
In large parts of Masuria and Warmia (Ermland), a referendum on the unification with Poland was to provide clarity. Even though an overwhelming majority had voted for East Prussia and thus for Germany, the mood on both sides was now charged with nationalist sentiments. Relations with the new neighbours were poisoned. East Prussians felt surrounded by enemies.
Illustration:
The voting areas of 1920
The distribution of German and Polish native speakers after the 1910 census and the results of the referendum for "East Prussia" in the relevant districts in 1920