What is the American sound?
Thereof, what makes Copland's music sound American?
The main characteristic that makes Copland's music so "American" is that America-themed media decided to use it as background music. I agree with the open fifths, that is the compositional answer here. The open fifths were adopted by several other composers to make an "American" sound.
Beside above, which composer is known for giving us the sound of America? Aaron Copland
Just so, what defines American music?
Americana is contemporary music that incorporates elements of various American roots music styles, including country, roots-rock, folk, bluegrass, R&B and blues, resulting in a distinctive roots-oriented sound that lives in a world apart from the pure forms of the genres upon which it may draw.
What music is American?
During this period the roots of blues, gospel, jazz, and country music took shape; in the 20th century, these became the core of American popular music, which further evolved into the styles like rhythm and blues, rock and roll, and hip hop music.