Final answer:
The Battle at Agincourt during the Hundred Years' War is significant in military history because of the successful use of longbowmen tactics.
Step-by-step explanation:
The Battle at Agincourt during the Hundred Years' War is significant in military history because of the successful use of longbowmen tactics. The English army, led by King Henry V, employed a large number of skilled longbowmen who were able to rain down arrows on the French army, causing significant casualties. This victory demonstrated the effectiveness of longbowmen in battle and showcased the potential of infantry over cavalry-dominated armies.