For nineteen years the Free City of Danzig was an independent city-state inside of the Polish-controlled Danzig corridor between Germany and its exclave of East Prussia. It stood as a reminder of Germany’s defeat in WWI and saw a great deal of tension between its German and Polish populations. In 1939, Germany demanded that Poland hand over the region and the city, and when Poland refused Germany invaded and on September 2nd took the city.
Following WWI, the Second Polish Republic gained independence and was given portions of eastern Germany. The most significant of these areas was the territory around Danzig. In order to be an economically independent state, Poland needed access to the sea and the city of Danzig was meant to be a neutral port city through which Poland would export and import goods. The Danzig constitution granted Poland the right to represent the city in foreign affairs, although the UK was given the duty of handling foreign relations, and further Poland had the final authority in economic decisions within the city, most importantly on tariff rates. A city police was established, along with a democratically elected senate which would manage domestic affairs. However, political instability was ever present. Although the Polish and German ethnicities were both granted equal rights, the two groups disliked each other with an intensity that only grew over time. By 1936 the Nazi Party gained a majority in the senate and the police were used to suppress political opponents and dissidents. The Danzig crisis began after the Munich Conference in 1938. Germany began to demand ever more control over the city and by 1939 clearly intended to use it as a pretext for war. The Danzig senate voted on August 23rd, 1939, to rejoin Germany, further increasing tensions. On September 1st, Germany invaded Poland and took the city the next day. Danzig was annexed into the German Reich, and would be occupied until 1945.
The history of the Free City of Danzig is an interesting tale of diplomatic compromise and competing nationalism. Realistically, the city could never have maintained its status for long as both German and Polish nationalists wanted to incorporate it into their respective nations. It served as a focus point for feelings of German revanchism, and was used by the Nazis to argue that Germany had been treated unfairly. Danzig is just one more example of how the Treaty of Versailles made another European war inevitable.