Answer: Because he is descripted as a furious soldier that must kill o be killed.
Step-by-step explanation:
Hi, in the red badge of courage, Henry is described as a war devil, because he has been described as a furious soldier that must kill or be killed and has no respect or sympathy for his enemies.
He shots with his rifle until it becomes hot, and keeps shooting even when the enemy has already withdrawn.
He is also called a fighting machine by his comrades.