The article never defines GDR, but I looked it up in case you were also unfamiliar:
The German Democratic Republic (GDR), commonly known as East Germany, was a socialist state in Central Europe that existed from October 7, 1949, to October 3, 1990
What an interesting slice of history.
The German acronym (DDR) is much better known among Eastern Europeans. My parents (Czech) would almost never call it East Germany.