This act of splitting off Prussia from Germany to give Poland access to the sea via Danzig would be the cause of WWII. 20 years after Poland took Danzig and all it's German speaking people Hitler would come to power in Germany. He brought amazing prosperity to Germany while Danzig lingered in depression under Polish rule. The people were German and wanted to reunite with Germany so they too could experience the economic boom happening in Germany.
Poland did not want to lose access to the sea which it had gained from taking Danzig and this led to animosity between the Polish rulers and the German people in the region. Pogroms began against the Germans in Danzig and by 1939 over 80,000 German refugees had fled their homes in Danzig to escape into Germany.
It was this conflict that led the Germans to invade Poland. But the Polish were setup by France and England to trigger this action when they told them they would be at their side if Germany tried to free the German people in Danzig and put an end to the pogroms ..... Poland was overrun with no help from anyone.
The tragedy here is that in 1920 Poland had actually saved Germany from the Bolshevik Russians and now they were fighting each other and letting the Bolshevik murderers take eastern Poland with the blessing of England and France who only declared war on Germany and did nothing to the communists who were doing exactly the same thing the Germans were doing..... Why? The Bolsheviks had already committed genocide in Ukraine where Stalin had starved 7,500,000 people to death to grow his communist armies. Why did England and France side with the communist murderers and ignore them taking Poland ?