More than twenty years after the Franco-Prussian conflict of 1870 and the Commune in 1871 when the Douanier Rousseau painted War, he was still very much affected by these events. In the centre, a grimacing female character holds a sword and a torch. This kind of Bellona, Roman goddess of war, rides a horse which looks more like a hybrid monster. The dark ground is covered with a pile of bodies, with crows feeding on this human flesh. The trees look charred. The clouds are red. Without any anecdotal or narrative elements, Rousseau conveys the drama in images. The large number of jagged shapes and the choice of colours, in particular, all contribute to this: the green of hope is completely absent; black and red, the colours of mourning and blood, dominate.

Among the possible sources for War, one borrowing is clear. The posture of the horse, a sort of "flying gallop", corresponds exactly to the pose of the horses in Géricault's Epsom Derby (1821, Paris, Musée du Louvre). However, thanks to the analysis of this movement through photography, it was known during Rousseau's time that this positioning was impossible, and never occurs during a horse's gallop. Hodler's Night can also be cited as a source. In this painting, which caused a great stir when it was exhibited at the Salon des Artistes Français in 1891, the bodies stretched out parallel to the plane of the painting, the range of colours and the presence of Death in the centre of the composition, are all elements which might have been suggested to Rousseau by Hodler.

At the Salon des Indépendants in 1894, War was received either with sarcasm, due to its heavy-handed appearance, or with enthusiasm as a result of its totally independent style. Thus, the young painter Louis Roy wrote in Le Mercure de France: "this picture may well appear strange because it does not evoke anything seen before. Is that not in itself a masterly quality? [Rousseau] has the rare merit today of having a style that is completely his own. He is moving towards a new art".