Many politicians and social groups use "fascism" and "nazism" synonymously, and this has confused me (and maybe others) for a long time. Is there any big difference between them, or are the differences so minimal that it's ok to use them as synonyms?
Fascism is the regime/ideology of anti-democracy. The state is absolute and totalitarian and all citizens must follow the state. Whether this applies just to a regime or also to an ideology advocating this form of regime, may be debatable.
National-Socialism or Nazism is a racist and antisemitic ideology which holds that the Aryan race is superior to all other races, and that the government must actively promote the perfect race.
Nazism tends to be fascist, but fascism is not necessarily national-socialist.
Edit: Some comments mention communism. In theory, communism is supposed to be democratic in the long run (the dictatorship of the proletariat is supposed to be just a phase), and many nominally socialist or communist countries pretended to be so (for example, the German Democratic Republic). The fact that in practice it became totalitarian and at times hard to distinguish from fascism (such as under Stalin) is an illustration of its failure. Fascism, on the other hand, is anti-democratic by design.
Fascism is a less broad ideology, and Nazism is more or less a superset of it (in other words, someone following Nazism as an ideology would likely subscribe to all the ideas of fascism, and a few extra ones that other non-Nazi fascists may not.
As a typical example, racial superiority ideas were part of Nazism, but not strictly speaking a major foundational part of fascism.
Please also note that scholars frequently distinguish fascism (a generic ideology) and capital-F fascism which was a specific variant of it as practiced by Mussolini's regime in Italy.
The main difference between Fascism and Nazism is rooted in the socioeconomic and sociopolitical climate of their country of origin, at the time they were developed, Italy and Germany respectively, which is deeply imprinted in both of them. fact that makes them unique
Both ideologies were developed to oppose currently dominant political or economic systems, in the case of Fascism: liberalism, Marxism, and anarchism and in the case of Nazism: communism, capitalism. Moreover, to provide a backbone to both nations and facilitate mobilization and militarization.
Having that in mind, they were probably developed carefully based on the specificities of the socium and the current mentality such that to resonate most with the masses, to remove polarizations, homogenise, purify (in the case of Nazism)1, morally rejuvenate, unite the nations and direct them towards a common "higher" goal.
1. Racial superiority: master race, the purest of the Aryan race was a major part of Nazism aimed, among others, to justify actions that couldn't be legally grounded.
Historically, Italian fascism* precedes nazism. It took power with the March on Rome in 1922.
When, in the following years and in other countries, movements of the same kind began to gain traction and international attention, they were compared to fascism.
The most notable was, of course, Hitler's National Socialist German Workers' Party, commonly referred to in English as the Nazi Party, which leaped in the German elections of September 1930 from 800,000 to 6,400,000 votes. Italian fascism was at the time well known and its dictatorship very well established. In the eyes of international observers, Nazism was a relatively new movement with much in common with fascism: I think that that's why they interpreted the events as Fascism rising in Germany as well **.
Fast forward, nazis have already taken over Germany and the term Fascism is used again to describe Franco's Falangism: volunteers from all over the world (like Robert Jordan in the famous For Whom the Bell Tolls) join the republican forces to fight the fascists in the Spanish Civil War.
And there have been many other instances again.
So we can now say that Fascism is commonly used more broadly to identify regimes, movements and ideologies while Nazism is strongly tied to Hitler's National Socialism. As Umberto Eco explained in his 1995 essay Ur-Fascism, this is probabilly not only because of historycal priority, but also because Nazism is much more coherent philosophically:
Mein Kampf is a manifesto of a complete political program. Nazism had a theory of racism and of the Aryan chosen people, a precise notion of degenerate art, entartete Kunst, a philosophy of the will to power and of the Ubermensch. Nazism was decidedly anti-Christian and neo-pagan
Contrary to common opinion, fascism in Italy had no special philosophy. The article on fascism signed by Mussolini in the Treccani Encyclopedia was written or basically inspired by Giovanni Gentile, but it reflected a late-Hegelian notion of the Absolute and Ethical State which was never fully realized by Mussolini. Mussolini did not have any philosophy: he had only rhetoric.
I would like to add that as an accuse, Nazi is usually perceived as stronger than Fascist. Partly because of all of the above: as a broader, fuzzier and less coherent term, Fascist may be considered weaker. Partly because of the different historycal courses that Italy and Germany had after WW2: Germany dealt with its past dictatorship while Italy didn't***. There were no Nuremberg trials for Italian war crimes, and many fascist administrators remained in charge after the war.
* Mussolini's National Fascist Party got its name from the former Fasci Italiani di Combattimento, best translated into "Italian Combat Leagues"
** For example, see Leon Trotsky's The fascist danger looms in Germany
*** See for instance Italy's Amnesia over War Guilt: The “Evil Germans” Alibi
The terms "fascism" and "fascist" are overused. Like several other words of political invective, their imprecise use stands as a substitute for thinking about the situation at hand, They are also anachronisms.
To conflate the two is a mistake leading to a grave misunderstanding of much of 20th century history. Fascism was ultra-conservative; accommodating of Church, monarchy, elites, and other elements of the ancien régime; and mindful of social hierarchy (the classes or orders of the corpus). The State was to be the beginning and end of political action, and matters such as race were secondary in importance. Nazism was radical and revolutionary. It co-opted, undermined, or defeated anciens régimes and aspired to transcend class by creating a unitary Volk. The state existed as a means to the racial end: race was all.
Both movements were, of course, militaristic and militantly nationalistic--and populist. We have seen hundreds of armed ultranationalist groups over the past century or more, and certainly the opponents in Ukraine fit this description. That does not qualify them as fascist. But the revolutions in Kiev and Simferopol have both been populist--and that designation is a the core of the question of legitimacy when an elected leader is ousted by popular action.
The descriptions for fascism here are apt however Nazism is a bit misunderstood as just being anti-Semitic totalitarianism which is only partially true.
Nazism - Nationalist Socialism (Nationalism and then Socialism), had its primary ideal as Nationalism (their definition that is) - thus requiring a pure and great nation. Which thus meant anyone who wasn't really German (i.e Aryan acc. to them) - Jews, Gypsies, other nationalities, even gays - was detrimental to the goal of greater Germany.
The Socialism part of it reflected this and instead of plain old Socialism (for equity for benefit of citizens), Nationalist Socialism though following the Socialist route of high state-control, state-run industries, housing etc. was more geared towards manufacture of goods that would primarily aid the nationalist goal - greater, stronger Germany which of course could've only been fulfilled by expansionist wars (so that Germans had more land to 'breathe').
Mussolini described the fascism saying 'nothing outside the state, nothing against the state, everything within the state'. It was a socialism movement where the state was a new god.
Since 30s most of the democratic states evolved in that direction, so the idea that the government controls or regulate every aspect of life is not controversial. However at that point the position of the government was much weaker and many people was fascinated with Mussolini's idea of creating perfect society by forcing people to act for a common good - the state. Maybe this opinion is controversial but fascist Italy didn't commit more crimes that e.g. british empire. There are many bad things you could and should say about fascism but it is hardly the worst thing ever.
National socialism is a german implementation of fascism mixed with racist definition of a nation. One lesson learned from German history is that they can't walk the middle of the street. The German fascist state was no competing against other countries, it was fighting other races.
Communists labeled all national or state governments as "fascist," including socialist democracies. I'm reading this in Cambridge political science professor Gareth Steadman Jones' notes in a book about the "Communist Manifesto" (Penguin, 2002).
The irony is that the communists themselves, by their own definition, were (or are?) "fascists" in that they believed in forcing all people--violently, if necessary--to become members of a global "state" or "nation," which brutally excludes all other states, nations, and political beliefs. Communists are textbook "fascists."
In other words, "fascist" is a term that the most rabidly passionate control freaks use to condemn and disparage all other control freaks.
National Socialism (otherwise known as its misnomer of "nazism") and Fascism are ideologically at opposite ends of the spectrum. Fascism is literally state corporatism, national socialism is... well, socialist.
National Socialism was staunchly against capitalism, and whilst it didn't oppose privately owned companies (unlike its 'cousin'/rival, communism), it did dictate that everyone (every German in "nazism's" case) was equal and was required to help one another and work for their nation and fellow Germans rather than personal gain.
I admit I am not as well versed with fascism, but it is effectively ultra-conservatism. In fascism, the state and corporations hold equal footing and the two work together to control the directions of the country. In theory this will create a very rich, powerful nation, however it is quite prone to corruption and generally has a very powerful military presence to go along with it.
Ultimately, Fascism and National socialism are not inherently evil ideologies like historians would have you believe, and they are certainly not the same. Hitler and Mussolini shared common beliefs, however, their methods of governing and priorities concerning the state were very different.