Throughout the later part of American history, and into modern times, the relationship between American and European music has been a discussed topic among scholars of American music. Some have urged for the adoption of more purely European techniques and styles, which are sometimes perceived as more refined or elegant, while others have pushed for a sense of musical nationalism that celebrates distinctively American styles. Modern classical music scholar John Warthen Struble has contrasted American and European, concluding that the music of the United States is inherently distinct because the United States has not had centuries of musical evolution as a nation. Instead, the music of the United States is that of dozens or hundreds of indigenous and immigrant groups, all of which developed largely in regional isolation until the American Civil War, when people from across the country were brought together in army units, trading musical styles and practices. Struble deemed the ballads of the Civil War "the first American folk music with discernible features that can be considered unique to America: the first 'American' sounding music, as distinct from any regional style derived from another country."