John Boyne's The Boy in the Striped Pajamas takes place in Nazi Germany. The main character, Bruno, moves with his family from Berlin to "Out-With," which is actually Gretel's way of pronouncing the name of one of Germany's most notorious death camps: Auschwitz. Gretel (Bruno's slightly older sister) explains:
I heard Father say that whoever lived here at Out-With before us lost their job very quickly and didn't have time to make the place nice for us.
Though the concentration camp bore this name, it was also the name of the town where it was located, on the border between two countries: Germany and Poland. Auschwitz had originally been Polish, but it was "incorporated within the German Reich" in 1939. It was not returned to the Polish until after World War II. The "extermination" (concentration) camp was built there in 1940.
Bruno's father originally works in Berlin, though Bruno is not sure what he does.
But when they asked Bruno what his father did he opened his mouth to tell them, then realized that he didn't know himself. All he could say was that his father was a man to watch and that the Fury had big things in mind for him. Oh, and that he had a fantastic uniform too.
For those familiar with the history of World War II and of Nazi Germany, "Fury" refers to the Fuhrer, the name by which Adolf Hitler, the leader of the Nazi movement was called.
The people Bruno and Gretel see from the window are boys and men:
There were small boys and big boys, fathers and grandfathers. Perhaps a few uncles, too.
As the inmates at Auschwitz were separated men from women, Bruno and Grete are only able to see the males. Later Bruno will meet the "boy in the striped pajamas," when he goes where he is absolutely not allowed to go—called "Out Of Bounds At All Times And No Exceptions." The boy's clothes are not pajamas, but a uniform issued to the captives at Auschwitz. The boy's name is Shmuel, and because he has a star on his "pajamas," the reader will realize that Shmuel is a Jew. Of all the races of people the Nazis endeavored to destroy, they passionately tried to exterminate the Jews more than any other group.
So the story is set some time after 1940, when the labor camp was built, but prior to the end of the war (1945) when those who remained alive at Auschwitz were freed by the Allies—in this case, the Red Army (soldiers of the Soviet Union). And Bruno's father is a member of the Nazi army.