Titus, My Brother by Frank Scalise

Appius and Titus, Roman soldiers, march toward Camulodunum to put down Boudicca's revolt. But the night before, Titus has some a pressing philosophical question for his brother-in-arms. It is one that Appius initially answers easily, but the more they discuss the question, the more he struggles for a true answer.
"Why do we fight?"
Before he can fully examine this compelling question, Appius and his cohort are thrust into combat against the fierce Iceni in a pitched battle for control of southern Britain.