Im going to have to agree with Des Essientes on this.
Although just to keep the discussion going...
Many different 'races' have walked in Europe. The majority of us are Proto Indo-European anyway which is why I dont like this argument.
You have the Vandali in that 'argument' area of land.
Some Vandali tribes were Germanic and some were also Slavic.
In this time period most of the land around there was simply called Germania but like I said both Germanic and Slavic people were in the area. Slightly east you had the Sarmatians.
The same is true for the Veneti tribes (also just east of the location).
A good portion of Germanic land was Slavic (including the Sorbs).
If you want to play the Germanic=German game, then Western Slavic=Polish.
By this time Poland is a "country". Nearby you have the HRE (which I personally would not call a country). Here in some of the disputed land you have the Obotrites, Veleti, etc which were mostly slavic.
Then you have Pomerania (one major city Szczecin/Stettin). Ah yes the place that Germans and Poles love to argue about. Well infact Pomerania held Germanic people, and slavic people (the Kushubian), and others. The fact is neither country had claim to this land (Germany who didnt actually exist and Poland who did not have full influence of the area). Afaik the cities origin is ~700/800AD.
Sorry to spoil everyones argument but I believe the country which first held Szczecin for a significant time was Denmark. See map of Europe in 1100 and 1200 for changes. And of course Poland and the states of the HRE (not Germany) fought for it many times.
;) Danzig was built by the Germanic tribes. If it was built by the Poles, they would have managed to create a decent fleet able to defend it. As of 16th century you still swam on rafts.
Please read my above post. Gdansk/Danzig area was inhabited by many peoples. We can go back thousands of years and its pointless. Poland actually made Gdansk into a real city before the Germans did.
In 980, Duke Mieszko I of Poland dedicated a fortress built in the region. The official year of foundation of Gdańsk (Gyddanyzc) was 997