The lieutenant tells Pete his father received the Medal of Honor in the Mexican-American War. But that medal wasn't created by Congress until the Civil War.
The Pawnee Indian tribes were "plains indians" occupying Nebraska & northern Kansas. They signed a treaty with the U.S. Govt, the last time in 1857. The Pawnee ceded land to the U.S. Govt in exchange for money, food as well as protection by Army forces against other inidian tribes.