The Other War is so called not to distinguish it from some better-known original Europian wars, but because the enemy (of pretty much everyone) was the mysterious Other. The first battle, if something so apparently one-sided can be describe as a "battle", was an attack on Castle Heterodyne, in which the Lady Lucrezia Mongfish Heterodyne disappeared for reasons still unknown, among many other casualties — including infant Heterodyne heir Klaus Barry. The Other primarily targeted sparks all over Europa, working through revenants, and managed to exterminate forty-three major houses and terrorize the whole continent. a turning point was the destruction of the 39th spark house a Lord Womack, the so-called "Lightening Eater". Bill and Barry Heterodyne appear to have led the resistance while searching for Lucrezia.
The war ended about a year later, concurrent with the Heterodyne Boys' disappearance, but after nearly two decades the aftershocks still haven't died away. Leftover revenants roamed the countryside until the Baron returned from exile in a very bad mood (and even after he eliminated those, there turned out much later to be a distressing number of sleepers); the disruption of the status quo must have been a major factor in the reigning violent chaos that prompted him to go conquering.