Many media outlets have recently started calling the war in Afghanistan the “longest war in United States history”. That statement is factually incorrect and they don’t care because it just makes things simpler by calling it the longest war. There are other wars which have gone on longer but have not had the continuous conflict of the Afghan war, which is actually what the media is referring to. The Korean War was never officially ended. An armistice was signed but there has been no official document which would end the state of war that existed between the United States and North Korea.
Oliver North has a few other examples in an article he wrote:
The U.S. Army’s campaigns against Geronimo, Cochise and other Apache leaders in New Mexico, Arizona and Texas went on continuously for nearly 40 years. Though Afghanistan has surpassed Vietnam in duration, it isn’t even our longest foreign military engagement. That distinction belongs to U.S. military operations during the Philippine Insurrection — which began concurrently with the end of the Spanish-American War, in 1898, and lasted until 1913. Notably, the number of U.S. casualties suffered in the Philippines — more than 7,100 — is approximately the same as the number of U.S. casualties to date in Afghanistan.