The First World War was an important caesura in the history of the province of West Prussia. The cornerstones negotiated in the Treaty of Versailles ended the integration of West Prussia into Prussian territory and incorporated the region into the newly founded Polish Second Republic. This led to major changes in the lives of hundreds of thousands of people of different origins, especially those already living and rooted there.
The Treaty of Versailles came into effect exactly 100 years ago. After the First World War had claimed millions of lives, the peace treaties between the “entente“ “entente“ Entente means an alliance or similar relationship between two or more states. France, England and Russia joined together by treaty in World War 1. Other states joined later. and the Central Powers - signed at the Paris Peace Conference - created a blueprint for lasting peace for Europe. However, the arrangements also led to radical political, economic and social upheavals. In particular, the territorial settlements brought about by the treaties led to enormous political and social upheavals. The force of the treaty settlements hit the German Reich hard. Among other cessions, it was above all the loss of territory in the East that had far-reaching political, social and economic consequences. For the province of West Prussia, the demand of the newly founded state of Poland for free access to the Baltic Sea had a particularly negative effect. Most of the province was ceded on the basis of the new peace provisions and formed part of the new state of Poland as the voivodship of Pomerania. When the treaty of Versailles entered into force on January 10 1920, the former province of 
West Prussia
deu. Westpreußen, pol. Prusy Zachodnie

West Prussia is a historical region in present-day northern Poland. The region fell to Prussia as a result of the first partition of Poland-Lithuania in 1772 and received its name from the province of the same name formed by Frederick II in 1775, which also included parts of the historical landscapes of Greater Poland, Pomerania, Pomesania and Kulmerland. The Prussian province lasted in changing borders until the early 20th century. After World War I, parts fell to the Second Polish Republic, founded in 1918. The largest cities in West Prussia include Gdansk (Polish: Gdańsk, today Pomeranian Voivodeship), Elbląg (Polish: Elbląg, today Warmia-Masuria Voivodeship), and Thorn (Polish: Toruń, today Kujawsko-Pomeranian Voivodeship).

 ceased to exist and hundreds of thousands of people left their homes. Only in a small part of the province was the population allowed to decide via a referendum in 1920 on the state affiliation of their region – here, as as in 
East Prussia
deu. Ostpreußen, pol. Prusy Wschodnie, lit. Rytų Prūsija, rus. Восто́чная Пру́ссия, rus. Vostóchnaia Prússiia

East Prussia is the name of the former most eastern Prussian province, which existed until 1945 and whose extent (regardless of historically slightly changing border courses) roughly corresponds to the historical landscape of Prussia. The name was first used in the second half of the 18th century, when, in addition to the Duchy of Prussia with its capital Königsberg, which had been promoted to a kingdom in 1701, other previously Polish territories in the west (for example, the so-called Prussia Royal Share with Warmia and Pomerania) were added to Brandenburg-Prussia and formed the new province of West Prussia.
Nowadays, the territory of the former Prussian province belongs mainly to Russia (Kaliningrad Oblast) and Poland (Warmia-Masuria Voivodeship). The former so-called Memelland (also Memelgebiet, lit. Klaipėdos kraštas) first became part of Lithuania in 1920 and again from 1945.

, over 90 percent of the people voted to remain part of Germany.