It was peacefully inhabited by members of both german and polish people, before the concept of nation states existed. That's where these names originate from.
At the end of the middle ages the cities voted (by war not by a referendum) to be part of the polish kingdom, because the polish king promised lower taxes. It was a conflict between the bourgeoisie in the cities and aristocracy in the country like everywhere in Europe, not between nations. Note that the polish king was an elected monarch, so not even the polish king was polish by the modern meaning.
In the 19th century there were national movements among both nationalities. After the first world war, people voted to be part of Germany, because it was richer and also more liberal, that's why the referenda were suppressed by the polish government. The regions were also full of coal or an important harbour, which is why the polish government cared about them beside national reasons. These actions were used by the nationalistic socialistic german workers party and others to justify hostile actions against the polish people. The polish government also expanded a police station on foreign soil into a military base against international treaties. After they also conquered official city buildings like the postal office, This led to the city major of Danzig calling for a military intervention, which was then expanded into the second world war due to the intention of the german government.
During the war slavic (including the polish) people were subject to murder, expulsion and the story with the concentration camps. After the war the polish army then did the same to the german people, including in regions were a large majority was german, which had been part of german states for centuries and which should become part of Germany again according to allied treaties. The plans originated back to before the war and were only called an answer to the German crimes to the public. These actions were objected to by the western allies, but were backed by the Soviets, because in-turn they could do the same to the polish people without the polish government objecting. This situation was what Churchill coined the term iron curtain about originally.
A lot of today's germans which insist on calling this cities by their german names are people which used to call it their homes (and still do). Some polish names were also only coined after the war, or coined earlier for propaganda but were never used until after.
Regarding the extermination camps: in contrast to the concentration camp they were only build on conquered foreign soil, because they didn't want to have these barbaric things in their home country and feared that it would cause outcry and objection by the German people (it was a dictatorship after all).
At the end of the middle ages the cities voted (by war not by a referendum) to be part of the polish kingdom, because the polish king promised lower taxes. It was a conflict between the bourgeoisie in the cities and aristocracy in the country like everywhere in Europe, not between nations. Note that the polish king was an elected monarch, so not even the polish king was polish by the modern meaning.
In the 19th century there were national movements among both nationalities. After the first world war, people voted to be part of Germany, because it was richer and also more liberal, that's why the referenda were suppressed by the polish government. The regions were also full of coal or an important harbour, which is why the polish government cared about them beside national reasons. These actions were used by the nationalistic socialistic german workers party and others to justify hostile actions against the polish people. The polish government also expanded a police station on foreign soil into a military base against international treaties. After they also conquered official city buildings like the postal office, This led to the city major of Danzig calling for a military intervention, which was then expanded into the second world war due to the intention of the german government.
During the war slavic (including the polish) people were subject to murder, expulsion and the story with the concentration camps. After the war the polish army then did the same to the german people, including in regions were a large majority was german, which had been part of german states for centuries and which should become part of Germany again according to allied treaties. The plans originated back to before the war and were only called an answer to the German crimes to the public. These actions were objected to by the western allies, but were backed by the Soviets, because in-turn they could do the same to the polish people without the polish government objecting. This situation was what Churchill coined the term iron curtain about originally.
A lot of today's germans which insist on calling this cities by their german names are people which used to call it their homes (and still do). Some polish names were also only coined after the war, or coined earlier for propaganda but were never used until after.
Regarding the extermination camps: in contrast to the concentration camp they were only build on conquered foreign soil, because they didn't want to have these barbaric things in their home country and feared that it would cause outcry and objection by the German people (it was a dictatorship after all).