What happens to a city when its demographics change completely in the space of a few years? To explore this question, we will take a look at the case of Danzig (modern-day Gdańsk) in northern Poland. The city's population was almost entirely German from its origin in the Middle Ages to World War 2. After the war, the population became Polish. To explore this question we will zoom out and look at these big issues: 1) The centuries-long eastern movement of Germans, who spread throughout central and Eastern Europe; 2) The establishment of the Free City of Danzig by Napoleon in 1807 after he dissolved the Holy Roman Empire; 3) Why Hitler wanted to capture Danzig immediately after invading Poland in 1939, even though it held no strategic value; 4) The expulsion of Danzig's German population after World War Two and how the city transformed with the importing of Polish residents, who renamed it Gdańsk. This episode is based on a question from listener Melissa, who wanted me to talk about the history of the city/city-state of Danzig before, during, and after World War II.