Name one war fought by the US in the 1900s?
The Philippine Insurrection 1899-1902. As of the 21st Century, the name has been changed to "Philippine-American War." This war was bloodier than the Spanish-American War of 1898 which had spawned it.
The Civil War! [EDIT] No! The Civil War was fought in the U.S. from 1861-1865. There were no U.S. wars fought in the decade of 1900-1909. The Spanish American War ended right before this decade began and World War One began in Europe in 1914. (We did not join World War One until 1918.) However, in this decade Russia and Japan were at war from 1904-1905.