France, June 21 -- Relations between Poland and Germany have been marked by a long and complicated history.

During World War II, Nazi Germany occupied much of Poland and killed nearly 6 million Polish citizens. After the war, much of Poland's territory was annexed by the Soviet Union.

One of the key sticking points to renewing ties was the recognition of the post-war border between Germany and Poland, the Oder-Neisse Line. While communist governments in Poland and East Germany agreed to move the border westward, West Germany resisted.

While there was a normalisation in relations between the countries in the 1970s, known as "Ostpolitik", the real turning point came with the collapse of communism and restoration of democracy in Poland in...