The gorgeously scruffy Juliette (director/cowriter Valérie Donzelli) and Roméo (cowriter Jérémie Elkaïm) — yes, the improbability is noted — move from dive-bar love-at-first-sight to proud parents of a newborn boy in the first few minutes of Declaration of War. Then their 18-month-old son, Adam, is diagnosed with a brain tumor. Shot in the actual hospital where Donzelli and Elkaïm's actual son was treated for cancer, Declaration of War turns autobiography into thrilling expressionist art. In other words, it's a "true story" that steers clear of aesthetic realism.
Always privileging feeling over story, Donzelli answers key questions via anonymous, clinical voice-over and condenses the passing of huge swaths of time into montage. This then frees her up to explore specific moments in the couple's struggle to cope with their son's sickness in microscopic detail, heightening Juliette and Roméo's moment-by-moment reactions to each obstacle.
Adam's diagnosis coincides with the 2003 invasion of Iraq, a fact Donzelli mentions outright once but mercifully doesn't strain to parallel. Although inherently narcissistic, Declaration of War is more generally about the emotional chaos of a prolonged struggle against an unfathomable threat. With baby Adam's fate a foregone conclusion (Donzelli and Elkaïm's real-life son plays "himself" in the first scene, clueing the audience in to the fact that both he and his fictional counterpart survive), the film is most successful as an exploration of the incomprehensibility of death in the mind of the living.