'The Hours Are Clear' is the fifth novel in the 'Rincewind' series of the 'Discosweet' series by Terry Pratchett.

During the centuries on the Opposite Continent, five noble homelands are vying for their own rule in the Empire. Then, it falls to the unknown “Great Enchanter,” who is our long-time acquaintance Rincewind, to unleash and complete the great war. Together with the army of their friend Koen the Barbarian, which consists of seven-year-old men, they fight against the bombarded and much larger army of the empire.

That's how it prepared The war is upon the heroes, and what can we overcome: strength, intelligence, what else?