Complex sentence: Carol M. Swain and Russell Nieli state that the white pride movement is a relatively new phenomenon in the United States, arguing that over the course of the 1990s, "a new white pride, white protest, and white consciousness movement has developed in America".
Split into simpler sentences: Carol M. Swain and Russell Nieli state the white pride movement is a relatively new phenomenon. They argue that over the course of the 1990s "a new white pride, white protest, and white consciousness movement has developed in America".