David Adamson Harper spent a number of years working in Panama in the maritime industry. During his first tour of duty there, the 1964 riots against American sovereignty over the Canal Zone occurred and he witnessed incidents in Colon at close hand. This created his interest in the history of the founding of Panama and the infamous Hay ̶ Bunau-Varilla treaty. He was amazed to learn how the treaty came into being and thereafter became a supporter of Panama’s aspirations to have it changed, and the Canal Zone returned to Panamanian sovereignty. 

During his second tour there, the Carter Administration agreed to renegotiate the treaty with the government of Panama, which led to the Carter ̶ Torrijos treaties and the return of the American Canal Zone and later the Canal itself. Harper spoke in favor of the new treaties, often in front of hostile American audiences. When the Canal Zone was returned to Panama in 1979 the State Department appointed him the United States Consular Agent in Colon, Panama.