When the United States entered the First World War, its troops were soon placed in an entirely new situation. For the first time in its history, American soliders were sent abroad in large numbers to fight along with foreigh allies against a common enemy. And no person holding any Office of Profit or Trust under them, shall, without the Consent of the congress, accept any present, Emolument, Office, or title, of any kind whatever, from any King, Prince, or foreign State.
Foreign medals fall squarely within the Constitutional prohibition.
Congress quickly passed legislation allowing American military personnel to accept foreign decorations, and during the First World War a large number of foreign decorations were awarded to Americans. Since then Congress has passed legislation permitting the acceptance of foreign awards from friendly foreign governments for specific periods of military action. However, the awards must have been presented and accepted by the recipient within the inclusive dates authorized by Congress. Decorations and medals offered to members of the Armed Forces must be one that is also conferred by the foreign government on its own armed forces. For example, South Korea created a medal intended for American military personnel who served in Korea during the Cold War.