What was the basis for the phrase the war of the blue and the gray?

The phrase "the war of the blue and the gray" refers to the American Civil War, symbolizing the Union (the North) and the Confederacy (the South) based on their respective uniforms. Union soldiers typically wore blue uniforms, while Confederate soldiers donned gray ones. This phrase encapsulates the conflict between the two regions and signifies the deep divisions within the United States during that period. It reflects both the military aspects of the war and the broader social and political struggles that defined the era.