So, as far as I know, categorizing people into different races and trying to assign different traits to them was a pretty big thing in the 19th and early 20th century, not only in germany, but all over europe.
If we look at Tolkiens universe, and look at his humans, we see that they are divided into different races of humans, which have a lot of distinctive traits. The humans of Numenor, for example, have a lot longer lifespan than other humans. The humans from the south are a lot easier corrupted by Sauron than other humans. The hobbits are also categorized as a human race and are very different from the others.
So my question is, is there any evidence if Tolkien supported race ideologies, and that is a reason for this categorization in his works? Or did he in genereal stated somewhere if he supports or oppsoses those ideas? I know that he clearly was against hitler, since he didn't want to release the hobbit in germany as long as he is in power, but what about the less radical ideas in that direction?
Anyway, I have in this War a burning private grudge—which would probably make me a better soldier at 49 than I was at 22: against that ruddy little ignoramus Adolf Hitler (for the odd thing about demonic inspiration and impetus is that it in no way enhances the purely intellectual stature: it chiefly affects the mere will). Ruining, perverting, misapplying, and making for ever accursed, that noble northern spirit, a supreme contribution to Europe, which I have ever loved, and tried to present in its true light.
It would have been impossible for Tolkien to have escaped racialist ideologies, given the times in which he lived. There are a few statements that showed he had absorbed some of the basic cultural stereotypes and used those in his writing (representing an inherent and probably unconscious bias); there are statements like the above which suggests he ascribed at least in part to the idea of a Northern/Aryan people that included the British; and there are some problematic aspects to how he developed his legendarium which reflect aspects of biology and, arguably, eugenics (the emphasis on royal lines, the breeding of orcs from elves, etc.).
We talked about this a bit in an earlier answer and the short answer is that Tolkien did base some of the peoples in his fantasy world on racial stereotypes. For example, he once wrote that orcs were:
[...] squat, broad, flat-nosed, sallow-skinned, with wide mouths and slant eyes; in fact degraded and repulsive versions of the (to Europeans) least lovely Mongol-types [...]
"Mongol-trypes" in this case referring to the racialist idea of Caucasoid/Negroid/Mongoloid; so basically he means "Asiatic," and you can see the parallel to Yellow Peril-style caricatures of Chinese and Japanese people.
Tolkien in an interview suggested:
The dwarves of course are quite obviously - wouldn't you say that in many ways they remind you of the Jews? Their words are Semitic obviously, constructed to be Semitic.
Meir Soloveichik argues the point further in The Secret Jews of the Hobbit. It should be emphasized that Tolkien, whatever stereotypes he might have held, Tolkien was opposed to the anti-Semitic stance of Hitler's Germany, as expressed in letters like:
But if I am to understand that you are enquiring whether I am of Jewish origin, I can only reply that I regret that I appear to have no ancestors of that gifted people.
In his later life, Tolkien is also known to have been opposed to apartheid in South Africa as well:
I have the hatred of apartheid in my bones; and most of all I detest the segregation or separation of Language and Literature. I do not care which of them you think White.
Strictly from a literary standpoint the decreasing lifespans of the Numenoreans is less an example of the scientific racialism of the period and more a callback to the Bible; you will recall that in the Genesis 5:5:
And all the days that Adam lived were nine hundred and thirty years: and he died.
...and his various descendants had progressively less lifespan until they met the Doom of Men; this was in keeping with the general theme of Tolkien's work of a kind of Golden Age, which slowly diminished as magic and wonder fled from the world, etc. and was common to other writers in the fantasy field, such as Lord Dunsany.
These overarching concepts are very influential on the final form of Tolkien's work, and it is in part why some of his conceptions are very problematic to contemporary eyes, where entire groups (orcs, trolls, uruk-hai, etc.) are categorized as "evil" and it's basically okay for the heroes of The Hobbit and Lord of the Rings to kill them. The morality of assigning entire groups in this way is quite stark, and resembles wartime propaganda quite a bit, but it also resembles the morality of fairy tales to a degree; it's notable that in the Silmarillion and other papers the morality gets a great deal grayer, closer to the Eddas in many ways.
It's harder to say much more about the various peoples of Middle Earth without succumbing to speculation; there are a lot of unanswered questions in Tolkien's legendarium, and he doesn't talk much about the men of the south, for example, focused as he is on the North and the elven-folks, and he doesn't generally try to directly tie different groups of Men or Elves to different national or ethnic stereotypes (it is not even clear that men and elves are much different physically, since their main differences appear to be spiritual), although the Rohirrim are based, linguistically at least, on Anglo-Saxons. The Hobbits in particular are a deliberate mystery as to their origins and heritage, in contrast with many of the other characters.
There's a vast secondary literature on all of this, and I don't have access to all of it, but I hope that helps answer your question. [/edit] Fixed interview link.
This is an excellent post. Follow-up question: which one was the bigger influence to Tolkien's writing - his own ideas of racial ideology, or his attempt to emulate classical particularly northern mythology, where this is very prevalent?
Reading the Nibelungenlied, I can't help but notice how closely it matched much of Tolkien's writing in terms of race relations. Surely that's not an accident.