Yellow fever decimated soldiers during the U.S. military occupation in Cuba (1898–1902), pressuring the U.S. Army to identify how it was transmitted. Cuban physician Carlos Finlay proposed the mosquito vector theory, which posited that yellow fever was spread by the Aedes aegypti mosquito. Initially skeptical, the Yellow Fever Commission eventually tested and proved his hypothesis. As a result, Cuba’s military governor, Brigadier General Leonard Wood, gave orders to dry out mosquito breeding grounds, swiftly eradicating the disease by the end of 1901.