28 Jul 1914—11 Nov 1918: World War I (WWI) This war spanned 4 years, 3 months, and 14 days. It began when Austria-Hungary declared war on Serbia on 28 July 1914 and officially ended with the armistice on 11 Nov 1918.
2
1939
1 Sep 1939—2 Sep 1945: World War II (WWII) This war spanned 6 years and 1 day. It began when Germany invaded Poland. The United States entered the war on 7 Dec 1941 when the Japanese attacked Pearl Harbor. Japan formally surrendered 2 Sep 1945.
3
1941
7 Dec 1941—2 Sep 1945: USA enters WWII The United States entered WWII when Japan attacked Pearl Harbor. The war ended with the surrender of Japan on 2 Sep 1945.
1917 -
