The map on page five is, while heavily distorted, definitely a map of europe, on top of that the humans (or the one human nation we've seen thus far) appear to be based on modern day germany, plus that guy having a german name, and what was clearly a concentration/death camp makes the pararell it's drawing pretty obvious, the map distortion gets worse further east but I'm mostly certain the fortress city captured in this chapter was St. Petersburg (named Leningrad in the hisory period I think they're going for)