All NAZI concentration camps were built originally to house political prisoners like socialists and communists. And later POW's. For example Auschwitz (well the first one anyway, there were 3) was built to house Soviet POW's in 1941. They didn't start to house Jews and other "undesireables" till later on. Soviet GULAG's (GULAG is actually an acronym for the NKVD branch that ran them) were built political prisoners. Most of whom had been kidnapped in the middle of the night. And shipped to a camp and held without trial for years on end. Stop me if that sounds familiar. Soviet GULAG's also housed criminals who's crime didn't warrant an imediate execution. And during WW2 Germans were also guests.

For fun GULAG means, The Chief Administration of Corrective Labor Camps and Colonies (bolds are where the letter for the acronym come from). And in Russian that comes out to GULAG.