White nationalism is not a recent phenomenon. The Klan and the Patriot Front being two current examples. Maybe the Proud Boys and the Oath Keepers?
Anyhow, look at the last thirty years of the nineteenth century. Organized or not, there were examples of white nationalism. Was there a mentality that this country
was put here for white people. Look at treatment of Native Americans and the New Immigrants. Develop a thesis that states either there existed or did not exist white nationalism in the US between 1870 and 1900.
as defined by the Southern Poverty Law Center: White nationalist groups espouse white supremacist or white separatist ideologies, often focusing on the alleged inferiority of nonwhites. Groups listed in a variety of other categories-KuKlux Klan, neo-Confederate, neo-Nazi, racist skinhead and Christian Identity-could also be fairly described as white nationalist.