It’s nationalism (the idea that different peoples deserve their own separate countries) with the people in question being white people. It manages to combine the most problematic aspects of nationalism such as its propensity to drive governments to commit countless atrocities with the most problematic aspects of whiteness as an identity. In short, it’s modern naziism.
What even is white? Like who is considered white seems to change every 5 or so years and the people in Europe usually don't even identify as white.
Like in my native language calling someone white doesn't even make sense or exist. Also calling someone back in my native language is actually insulting since black and dirty are the same word and people assume the former.