Here's why:
* Symbolism in poetry uses objects, images, or ideas to represent something else, usually something abstract or complex.
* The American flag is a tangible object, but it represents concepts like freedom, patriotism, unity, and the nation itself.
While the flag itself isn't a poem, its use in poetry would be an example of symbolism. For instance, a poem about the American Civil War might use the flag to symbolize the conflict between North and South.