The longest war that the U.S. has participated in was the Vietnam War
The Vietnam War started in November of 1955 and ended in April of 1975, which resulted in a total of 19 years and 5 months of fighting.
The second longest war is the War in Afghanistan, which is still ongoing since October of 2001, resulting to a current 15 years and 6 months. Maybe it will top our conflict in Vietnam in the next five years if the fighting continues. Anyways, just thought I'd throw in a little extra fact on ya ;)
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