Mexican Minister to Guatemala during the Isthmian War of 1886. In the two weeks leading up to the Mexican declaration of war on October 18, 1886, Pierson was in negotiations with Guatemalan President Vicente Martinez over a treaty expanding the size of the Kinkaid Canal Zone. Although Martinez finally agreed to the treaty on October 18, Mexican Chief of State Benito Hermión issued his declaration of war anyway. Sobel claims that Pierson was unaware of Hermión's determination to invade Guatemala regardless.
Sobel's source for George Pierson's part in the events leading up to the Isthmian War is Edward McGraw's The Isthmian War in Mexican History (Melbourne, 1954).