The United States of America (most commonly abbreviated USA) is the country where the Simpsons and most of their friends live. USA is located in the Western Hemisphere, along with the Northern Hemisphere. From 1775 to 1783 it fought in the American Revolution. Next, from 1861 to 1865, it fought in the Civil War. Later, from 1941 to 1945 it fought in World War II. And finally, from 1963 to 1973, it fought in the Vietnam War.
Since America is the setting of the Simpsons' family, all episodes at the very least either briefly show America, have America in the opening sequence or locations can be automatically assumed as American.