The term 'Nepal' is first found in 'Atharva Parishista' (4th Century B.C.). The term 'Kirat Pradesh'
can be found in earlier documents. According to this, it is understood that the term 'Kirat' not only stands for Rai, Limbu or Sunuwar but also stands for all the people living here at that time, including
the Newars and Tharus.
Points to be taken: It is striking that the present ethnic group of Nepal including Rai, Limbu, etc
has virtually no earlier history in ancient literature. There are no instances of any of the group occurrence in the Vedic literature. The epics are similarly barren: neither the Ramayana nor the Mahabharata give evidence any group solely belonging to Kirat. Hence the Kirat denotes the Tibeto-Burmese people and the aborigines of Nepal as described below;

The term Mongoloid viz Tibeto-Burmese is relatively new coined by scholars to classified people.
The term Kirat on the other hand is a corrupt form of Kiriat, Kiryat or Kirjath which means a fort
or town in Moabite language of the Mediterranean region. Sir John Hammerton in his book called “Early Races of Mankind", mentions that probably in the 4000 BC, there was a civilized race of mankind on the lower Euphrates of the Mediterranean region described as Mongolian or
Summerian of the Cheldean.

In the ancient hindu scriptures such as veda, the mongoloid looking people were called KIRATAS.
Here's some quote from the book KIRATA-JANA-KRTI by Suniti Kumar Chatterji.
The name Kirata is for the first time found in the Yajurveda (Sukla Yajurveda, Vajasaneya, XXX, 16;
also Krsna Yajurveda, Taittiriya Brahmana, III, 4,12,1). In connexion with the Purusa-medha or ‘Man-Offering’ sacrifice, where a
list of all kinds of human beings and animals symbolically or
figuratively offered to the gods as sacrifice is given, we find the
following passage:–
guhabhyah Kiratam; sanubhyo Jambhakam; paravatebhyah Kimpurusam
which upon translation will read ‘A Kirata, for the caves; a Jambhaka (long-toothed man) for the slopes; a Kimpurusa (an ugly man, a wild man, an ape) for the mountains.’

Then in the Atharvaveda (X,4,14) we have a reference to a Kirata girl
(Kairatika) who digs a herbal remedy on the ridges of the mountains:–
Kairatika kumarika saka khanati bhesajam:
hiranyayibhir abhribhir girinam upa sanusu.
upon translation
‘The young maid of Kirata race, a little damsel, digs the drug:
Digs it with shovels wrought of gold on the high ridges of the hills.’ (Translation by R.T.Griffith.)

‘Kirata is a name applied to a people living in the caves of the mountains, as appears clearly from the dedication of the Kirata to the caves in Vajasaneyi Samhita (also Taittiriya Brahmana), and from the
reference to a Kirata girl, who digs a remedy on the ridges of the mountains.
Therefore the Vajasaneyi Samhita of the Shukla Yajurveda refers to the Kiratas as cave dwellers.

KIRATAS are described in the ancient text as 'gold-like', i.e, yellow in color (and not dark or black like the Dasas and Dasyus and the Nisadas(residents of present-day Africa)

Here's the quote from the the book taken from Kirata-parvan section of Varna-parvan of the Mahabharata.
Kairatam vesam asthaya kancana-druma-sannibham
"Taking up a Kirata resemblance, like unto a tree of gold" (IV,35,2);
dadarsatha tato jisnuh purusam kancana-prabham
"Then the Victorious One(Arjuna) saw a Man, shining like gold" (IV, 35,17);
na tvam asmin vana ghore bibhesi kanaka-prabha
"O thou that art shining like gold (addressing Siva in the form of
Kirata), dost thou not fear in this terrible forest" (IV, 35, 18)

The Ramayana also mentions the golden color of the Kiratas; thus
Kiratasca tiksna-cudasca hemabhah priya-darsanah,
antar-jala-cara ghora nara-vyaghra iti srutah
upon translation is The Kiratas, with hair done in pointed top-knots, pleasant to look upon, shining
like gold, able to move under water, terrible, veritable tiger-men, so are they famed.

In Sanskrit, Kirata means one wandering over the forests with "kiram atati bhramati yah" hence denoting the Adivasi Janajatis (Indigenous Nationalities) of Nepal,
thereby solving the issue of “Unity, not ethnic, division”.  Now this is true_beauty_of_Nepal.