Final answer:
Native Americans significantly contributed to WWI through combat service and as code-talkers, using their languages to create secure communication codes.
Step-by-step explanation:
During World War I, Native Americans were noted for their critical roles in various aspects of the war effort. Specifically, they were known for their combat service in the army, which included leaving their reservations and integrating with other servicemen. However, one of the most prominent and unique contributions made by Native Americans, particularly the Choctaw during WWI and the Navajo, WWII, was their use as code-talkers. These code talkers utilized their native languages to create unbreakable codes for transmitting military communications, proving to be an invaluable asset in maintaining the confidentiality and integrity of Allied communications.