Anarchism

The most useful definitions of fascism I've seen are how it's primarily a response to a collapse in liberal economic order and certain sectors of capital find it useful to rile up popular suppression of leftist organizing. As in, capitalists hit the emergency button to maintain authority and drop the theater of democracy. In some cases fascists will represent specific sectors of capital, such as manufacturing, at the expense of other sectors such as finance. The ethnic superiority thing comes along with typical revanchist rhetoric about restoring order, which is the main plank of a standard fascist movement: "We'll get rid of the socialists and restore the previous order."

I really do think it's most practical to view fascism as an emergency movement. It's panic, it's frenzied stripping of the copper wires. Not to get into it here, but "peacetime" fascism is arguably modern neoliberalism.

I typically point to Robert O. Paxton's work. He's a liberal, but otherwise has a very good insight into fascism.