Chinese Wild Claims in Arunachal

McMahon Line signed by Lochen Shatra and Sir Henry McMahon

The Chinese are not happy at all. Why?
Because the Japanese foreign minister Fumio Kishida dared to speak about what Beijing calls "a Chinese territorial area adjacent to India as Indian territory."
According to The China Daily, the Japanese diplomat was referring to Arunachal Pradesh.
Beijing immediately lodged a strong protest: "We hope Japan fully understands the sensitivity of the China-India boundary question," said Foreign Ministry spokesman Hong Lei.
He added that in a speech in New Delhi, "Kishida attracted media attention after referring to a southern area of China's Tibet Autonomous Region as Indian territory. ...Beijing has taken notice of the report, expressed serious concerns, demanded Japan make a clarification and immediately manage damage control."
Unfortunately for Beijing, the bullying tactics do not work with Japan.
Hong however affirmed that Tokyo had earlier stated its position of "no taking sides in regard to the areas disputed by China and India" and promised Beijing that it will not get involved in the issue.
Beijing requested Tokyo to "pay due respect to efforts made by China and India in resolving disputes through negotiations and be cautious with words and actions when it comes to the issue," as the two countries (China and India) are "seeking a fair, reasonable solution that will be acceptable to both sides."
The website China Tibet Online explains: "Arunachal Pradesh, which includes three areas in Tibet Autonomous Region -- Monyul, Loyul and Lower Tsayul, is currently under Indian illegal occupation. The Chinese government's stance on these areas, located between the illegal 'Mcmahon Line' and the traditional customary boundary between China and India, is that they have always been Chinese territory."
Historical facts say differently.
First of all the McMahon Line is very much legal: it was signed by the Prime Minister of Tibet (Lochen Shatra) and India's Foreign Secretary (Sir Henry McMahon) in March 1914 (see map above).
As importantly, during the last two millennia, the Chinese have never set a foot in what is today Arunachal Pradesh (former NEFA), except for one short visit in one particular location in 1910.
To quote from my book, 1962: the McMahon Line Saga:

Soon after their occupation of Lhasa [in 1910], Zhao Erfeng’s [Chinese warlord] troops undertook the subjugation of Poyul, the region located north of the territory inhabited by the Abors in the Yarlung Tsangpo/Brahmaputra Valley. Zhao Erfeng invited Chinese settlers to come and settle in Zayul, near Rima on the Tibetan side of the Lohit valley.
The British knew what was going on.
In the decades to come, the entire North-East policy would be based on the Chinese threat [in this area].
During the summer of 1910, some Chinese troops were posted near Rima. They went as far south as Walong where they planted boundary flags, in a place where the Lohit joins the Yepuk river.
This incident rang the bells in Delhi and London. Something had to be done.

A brief intrusion in the Lohit valley does not means that the entire NEFA has always belonged to China, but it is what Beijing pretends today.
In any case, the  so-called boundary markers were soon removed by the British.
I again quote from the McMahon Saga (note that the British called their small expedition a 'promenade'):

The Walong Promenade and the Chinese Cairns
On November 19, 1913, the Secretary of State sanctioned a new ‘promenade’. T. P. M. O'Callaghan, the Assistant Political Officer, Sadiya was in charge. He was accompanied by an escort of the 1/8th Gurkha Rifles led by Major C. Stansfeld and Lt. H. R. Haringlon.
The British officers visited Rima at the invitation of the Tibetan authorities, and apparently cordial relations were established.
On May 6, 1914, Sir Archdale Earle, the Chief Commissioner of Assam writes: "Mr. O'Callaghan's report confirms the information in the possession of the Chief Commissioner that there are at present no Chinese troops anywhere in the neighbourhood of Rima. It urges nevertheless the importance of carrying the Lohit Valley road to our frontier, and of establishing a post as near the frontier as is practicable at the earliest possible date. This view is shared by the Chief Commissioner, but he realises that, for reasons which will presently be stalled, it will probably be found advisable to move slowly in the coming cold weather. He thinks, however, and he trusts that the Government of India will agree in this view, that the impossibility of recognising a Chinese boundary in the neighbourhood of Menilkrai has been finally established, and he regards Mr O'Callaghan's action in removing the boundary posts as thoroughly justified."
The APO had found Chinese markers at a place called Menilkrai, just below Walong. One set dated from 1910 and new markers had been placed in 1912 by the Chinese troops. O'Callaghan removed the markers, repositioned them upstream, near Kahao just south of the McMahon Line.
O'Callaghan confirms that a post needs to be established at Walong: "I am more than ever convinced of the necessity of the finishing of the road to our frontier and the opening of a post as near our frontier as soon as possible. From Walong to Rima, there is no difficulty in road making and the Lohit Valley road already constructed and open up to Mankum only required continuation to Manglor flat, a distance of less than 30 miles, to make the opening and rationing of the post a practicable scheme."

Even before the McMahon Line was formerly delineated, there were no Chinese presence in NEFA.
It is however true that there were areas where the Tibetans had some influence (it represented some 10% of the NEFA's territory); it was mainly in Tawang area, in today's West Siang [Pachaksiri], Upper Siang [Tuting, Geling], and Lohit/Anjaw, where tribes affiliated with the Tibetans (Monpas, Mempas, etc...) lived.
This again does not make Arunachal 'Chinese' as the Chinese never even visited these areas.
It is however true that the shyness of the Government of India which still insists on an Inner Line Permit (or Protected Area Permit for foreigners) encourages the Chinese government to continue with its wild claims.
Delhi should assert once and for all that the entire Arunachal is Indian and therefore treat at par with the other Indian States and every Indian national should be allowed to freely visit the State (while, of course, keeping in mind security issues at the proximity of the border with China).