For those unfamiliar, The Pushcart War is a children's book by Jean Merrill, copyright 1964, with illustrations by Ronni Solbert, who was Merrill's partner for almost 50 years. It's framed as a history, but the dates of the events recounted are in the future, and they stay in the future, moving forward in time in every edition.

This is why I say it is science fiction, or at least speculative fiction: it imagines a possible uprising against oppression and tells that story as though it had already happened, from the perspective of a future in which the oppressors are totally unknown to young children. That's where the book begins: with a Forward (by an imaginary professor) about the importance of understanding how wars start.

The Foreword is explicit about the story being a metaphor "For big wars are caused by the same sort of problems that led to the Pushcart War." (The imaginary professor then praises the author's research while mentioning one small imaginary error in an imaginary statistic).

Then there's an introduction, signed by Jean Merrill, which emphasizes the importance of children, particularly, understanding how wars start. In the edition I'm reading now, this introduction is dated October 14, 2036, and the Pushcart War takes place in 2026.