All this happened, more or less

So Kurt Vonnegut assures in the preface to the book. All the characters from the war parts of the novel are real (except for their names, of course), there really was a guy who was shot in Dresden for taking a teapot that wasn't his, as was the dying colonel whose last will was to call him Wild Bob. To enhance the sense of reality the author even puts himself in the book as an episodic character, some kind of literature cameo.

The description of German prison camp strikes by its naturality and ferocity. Billy Pilgrim with the rest of the Americans were newcomers there and they met English and Russian captives. A great difference between them is shown, the Russians were held in horrible conditions, while the Englishmen lived in proper buildings, had lots of food, coffee, sugar, chocolate and had trade relationship with their captors. "Slaughterhouse-five" is to be taken  as a significant war novel at least because American historians don't expatiate upon the bombing of Dresden.

As contrasted with the war storyline, Billy's life after that is shown as useless, lazy and sick existence, as an example of the Second Lost Generation. Billy Pilgrim married for convenience, got rich, had two children who didn't take him seriously, worked as an optometrist who took a nap right on the appointment with patient.

The narration in the book is well-balanced, following episodes are judiciously connected notwithstanding huge time gaps between them. For example the episode when Billy is taught to swim by sink-or-swim method by his father corresponds with disgusting description of being washed by Germans with the rest of the captives with cold water in the prison camp.