Final answer:
The United Nations was formed in April 1945, and it began peacekeeping missions shortly thereafter. The exact year the United Nations Service Medal was authorized is not specified within the provided information.
Step-by-step explanation:
The United Nations Service Medal was authorized after the establishment of the United Nations, which was officially formed in April 1945. However, the specific year when the Medal itself was authorized is not provided in the information given, and as such, I cannot provide an accurate year. The United Nations has been actively involved in peacekeeping missions since the late 1940s to fulfill its pledge "to save succeeding generations from the scourge of war."