Lots of wars were fought by the United States in the 20th Century:  1. Philippine Insurrection (Philippine-American War 1900-1902). 2.  WW1 (1917-1918) 3. Banana Wars (Centr…al/South America)  1920's/1930's 4. WW2 (1941-1945) 5. Korean War (1950-1953) 6.  Vietnam War (1961-1975) 7.