Danzig(Polish Gdansk), a city on the Baltic Sea, held alternatively by Germany and Poland.
After WWI Danzig was made a "free city" under the auspices of the League of Nations. This gave Poland access to the sea and cut off East Prussia from the rest of Germany. Over ninety percent of the population was German and wanted to be re-united with Germany.
In the elections of 1933 the fascist National Socialists became the leading political power. Anti-Semitic policies were enforced. Danzig was reunited with Germany on September 1, 1939 with the outbreak of WWII.
Source: Encyclopedia of the Holocaust.