The piece of written work that starts with the line "All this happened, more or less." is the novel "Slaughterhouse-Five" by Kurt Vonnegut. Published in 1969, "Slaughterhouse-Five" is a satirical and semi-autobiographical novel that explores the experiences of the protagonist, Billy Pilgrim, during World War II and his subsequent time-traveling journeys. The opening line sets the tone for the novel's blending of fact and fiction, as Vonnegut himself was a prisoner of war during the bombing of Dresden, an event that heavily influences the narrative.