Final answer:
The quote 'Tempered by war, disciplined by a hard and bitter peace' uses a metaphor as a rhetorical device.
Step-by-step explanation:
The rhetorical device used in the quote, 'Tempered by war, disciplined by a hard and bitter peace', is a metaphor. A metaphor compares two things by saying they are the same. In this case, it compares the experience of war and peace to the process of tempering and disciplining. War is compared to 'tempering' and peace is compared to 'disciplining'.