Mark Mazower in his book Hitler's Empire Nazi Rule in Occupied Europe wrote that even Hitler himself believed in the same idea:
Page 160."Hitler himself talked about a Mongolensturm, while German propaganda referred to the 'spineless Slavic-Mongol pap' that compromised the human matter of the USSR. Sometimes it sounded as though Barbarossa was a duel between Goths and Nordic peoples on the one hand and Tatar Untermenschen on the other. These racial stereotypes played an important role in the targedy that unfolded.
And, Hitler did indeed speak of a 'Mongolensturm' during WW2:
Hier hat sich gegen Europa eine Macht zusammengeballt, von der leider die meisten keine Ahnung hatten und viele heute noch keine Ahnung besitzen. Es ware dies ein zweiter Mongolensturm eines neuen Dschingis Khan geworden. DaB diese Gefahr abgewendet wurde, das verdanken wir zunachst der Tapferkeit, der Ausdauer und Opferwilligkeit unserer deutschen Soldaten und dann auch den opfern aller derer, die mit uns marschiert sind. Denn zum erstenmal ist diesmal doch so etwas wie ein europaisches Erwachen durch diesen Kontinent gegangen.
Here a power has come together against Europe, of which unfortunately most of the people had no idea and which many today have no idea. It would have been a second Mongol storm by a new Genghis Khan. We owe that this danger was averted first of all to the bravery, perseverance and willingness to make sacrifices of our German soldiers and then also to the sacrifices of all those who marched with us. Because for the first time something like a European awakening has passed through this continent.
Sie kennen unsere Verbundeten, angefangen vom Norden das tapfere kleine Heldenvolk der Finnen, das sich wieder so tiber alle MaBen bewahrt hat. Aber dazu sind dann gekommen Slowaken, Ungarn, Rumanen und endlich Verbundete aus ganz Europa: Italiener, Spanier, Kroaten, Hollander, danische Freiwillige, selbst franzosische und belgische Freiwillige. Ich kann wirklich sagen, daB im Osten vielleicht zum ersten Male in einer gemeinsamen Erkenntnis ganz Europa kampft: so wie einst gegen die Hunnen, so diesmal gegen diesen Mongolenstaat eines zweiten Dschingis Khan.
You know our allies, starting from the north with the brave little hero people of the Finns, who have once again preserved themselves beyond all measure. But then there were Slovaks, Hungarians, Romanians and finally allies from all over Europe: Italians, Spaniards, Croats, Dutch, Danish volunteers, even French and Belgian volunteers. I can really say that in the East perhaps for the first time all of Europe is fighting with a common understanding: as once against the Huns, this time against this Mongol state of a second Genghis Khan.
Himmler declared during WW2:Von Monat zu Monat mehr wurde schon im Jahre 1940 die Erkenntnis gewonnen, daB die Plane der Manner im Kreml bewuBt auf die Beherrschung und damit Vernichtung ganz Europas hinzielten. Ich habe der Nation schon ein Bild des Aufmarsches der russischen militarischen Machtmittel im Osten gegeben, zu einer Zeit, in der Deutschland nur wenige Divisionen in den an RuBland angrenzenden Provinzen besaB. Nur ein Blinder konnte es ubersehen, daB sich hier ein Aufmarsch von weltgeschichtlich einmaligen Dimensionen vollzog. Und zwar nicht um etwas zu verteidigen, was nicht bedroht war, sondern nur um etwas anzugreifen, was zur Verteidigung nicht mehr fahig zu sein schien. Wenn die blitzartige Beendigung des Feldzuges im Westen den Moskauer Machthabern auch die Moglichkeit nahm, mit einer sofortigen Erschopfung des Deutschen Reiches rechnen zu konnen, so beseitigte dies keineswegs ihre Absichten, sondern verschob nur den Zeitpunkt des Angriffes. Im Sommer 1941 glaubte man den gunstigsten Moment des Losschlagens zu sehen. Nun sollte ein neuer Mongolensturm tiber Europa hinwegbrausen.
From month to month, as early as 1940, the realization was gained that the plans of the men in the Kremlin were deliberately aimed at the domination and thus the destruction of all of Europe. I have already given the nation a picture of the deployment of Russian military power in the east at a time when Germany had only a few divisions in the provinces bordering Russia. Only a blind man could overlook the fact that a march of dimensions unique in world history was taking place here. And not to defend something that was not threatened, but only to attack something that no longer seemed capable of defending itself. If the sudden termination of the campaign in the west also deprived the Moscow rulers of the possibility of an immediate exhaustion of the German Reich, this in no way eliminated their intentions, but only postponed the time of the attack. In the summer of 1941, it was believed that the most favorable moment to strike was seen. Now a new Mongol storm was about to sweep across Europe.
Mark Mazower, Hitler's Empire Nazi Rule in Occupied Europe, page 194.An aesthete, like many racists, he attached great importance to physical appearance. 'The racial enquiry should prevent the development of Mongol types in the newrly settled East,' he ordained. 'I want to build a blond province here.'
Himmler declared during a speech to SS soldiers in July 1941:
As late as 1944, Himmler was still claiming similar things:It is a war of ideologies and struggle races. On one side stands National Socialism: ideology, founded on the values of our Germanic, Nordic blood. It is worth the world as we want to see: beautiful, orderly, fair, socially, a world that may be, still suffers some flaws, but overall a happy, beautiful world filled with culture, which is precisely Germany. On the other side stands the 180 million people, a mixture of races and peoples, whose names are unpronounceable, and whose physical nature is such that the only thing that they can do - is to shoot without pity or mercy. These animals, which are subjected to torture and ill-treatment of each prisoner from our side, which do not have medical care they captured our wounded, as do the decent men, you will see them for yourself. These people have joined a Jewish religion, one ideology, called Bolshevism, with the task of having now Russian, half [located] in Asia, parts of Europe, crush Germany and the world. When you, my friends, are fighting in the East, you keep that same fight against the same subhumans, against the same inferior races that once appeared under the name of Huns, and later - 1,000 years ago during the time of King Henry and Otto I, - the name of the Hungarians, and later under the name of Tatars, and then they came again under the name of Genghis Khan and the Mongols. Today they are called Russian under the political banner of Bolshevism.
Peter Longerich, Heinrich Himmler: A Life, page 263.An Atilla was born in this seething mass of millions of subhumans, in the same way suddenly in some couple of two people the spark can be ignited by means of which an Atilla, a Genghis Khan, a Tamberlaine, a Stalin can emerge from lost traces of Nordic-Germanic-Aryan blood that is floating in this mass and which alone can give rise to powers of leadership and organization.