To pass the time he told his companions stories: when he came home in 1945 he found a publisher for a book of them, I Scarabocc (Cockroaches, but also "scribblings").
At 30 he moved to Rome and worked as a schoolteacher. During this time he met Elio Petri, the Future Director of Investigation of a Citizen Above Suspicion (1970), who worked as assistant to Giuseppe De Santis. Guerra was able to get his first screenwriting credit after he and Petri went to the Abruzzi mountains to find out about wolf-hunting; "Though they discovered that wolf Hunters no longer existed, De Santis went ahead anyway with the film, Uomini e Lupi (Men and Wolves, 1957)".
In 1990 Guerra in collaboration with Giovanni Urbinati to create the exhibition “La Cattedrale dove va a dormire il mare/The Cathedral where the sea goes to sleep” at the deconsecrated church in Budrio near Bologna.
In 1995 he was awarded with an Honorable Diploma at the 19th Moscow International Film Festival.