Nazism is a racial supremacist ideology that bases the roots for its ethos in Germanic and Nordic racial heritage and utilises a top-down authoritarian political model. Whereas Fascism is a militaristic, populist, traditionalist ideology which the aim of it's system is to order society in the pragmatic design that closely aligns with not only human behavior and organisation but also natures design. Fascism is in essence a modern rendition of natural human tribalism and feudalist structure.
While Fascism and Nazism (specifically the original National Socialism, not referring to modern reeditions of the term) are both very similar, it is folly to regard the two in the same way or as being interconnected. Considering Nazism and Fascism in the same vein is just as incorrect and ignorant as calling Socialism and Communism the same, because they are similar in ethos and apperence.
Nazism is best defined by it's brutal and horrific eugenics that put not only particular racial groups or perceived racial groups above others but also for it's inherent barbarism and survival of the fittest philosophy that is core to it's philosophy. Nazism is an unhinged animalistic ideology that is not only brutal, but inherently expansionist in pursuit of it's goals making it one of the most dangerous and vile ideologies ever thought of.
Fascism by contrast has no inherent racial ideology at all and is focused solely on ideological superiority over genetical competition. Fascism has no inherent expansionism and is instead nationalist.
Nazism based it's militarism and style off of Fascism-proper hence why they are visually identical.
In short, the biggest difference between Fascism and Nazism is that Nazism is a racist and ableist ideology that prioritises racial purity whereas Fascism is simply a pragmatic ethos that prides power as a tool of order and stability.
I shouldn't have to say this but nazis are bad.
