First sentence: No, it wasn't. It was after pakistan sent pashtun marauders into kashmir and started plundering and invading the people, that the maharaja ran to India for help. India accepted on the condition that the state would accede to India. The instrument of accesion was signed, and Indian troops stopped the pakistani lashkar/tribal invasion of kashmir, and retained the other part that had not yet fallen to the marauders.
It was pakistani lashkars that invaded kashmir first. That's on historical record.
Lets not use the indian timeline of events which start from the "tribal invasion" but the real time line.
On November 5 and 6, 1947, more than 100 lories, loaded with women, children and old men were taken into the wilderness of Kuthua forests. Hindu extremists and armed gangs were let loose on these innocent people and an unparallel butchery was perpetrated,
British daily The London Times quoting its special correspondent in India stated that the Maharaja, under his own supervision, got assassinated 2,37,000 Muslims, using military forces in the Jammu area.
The editor of Statesman, Ian Stephen, in his book Horned Moon writes that till the end of autumn 1947, more than 200,000 Muslims were murdered in one go. Horace Alexander wrote in the Spectator (16 January 1948) that the killings had “the tacit consent of State authority” and put the figure at 2,00,000.
Times of London reported the events in Jammu with such a front page headlines: “Elimination of Muslims from Jammu”, and pointed out that Maharaja Hari Singh was “in person commanding all the forces” which were ethnically cleansing the Muslims.
Daily Telegraph of London dated 12 January 1948
The other aspect of the carnage was appropriation of properties of Muslims. The Muslim names were immediately erased to conform to new ownership. For instance Urdu Bazar became Rajinder Bazar and Islamia School became Hari Singh High School to conform to the new “ownership”. Almost 95 percent of left-over properties, which should have in the normal course been taken over by the State government were allowed appropriated by looters and rioters
So that gives you an idea of what was going on before any "tribal invasion".
Patiala State infantrymen stationed at Jammu and Patiala gunners positioned at Srinagar Airfield on 17th of October 1947 could not have gone unnoticed
So the excuse that the indian army only came in after the "tribal invasion" is false.
It was only after the mass killings that the Muslims soldiers from poonch-mirpur had a uprising against the Dogra regime for its connivance in the ethnic cleansing of Muslims in kashmir. They knew that the Dogra regime intended to accede to India and New Delhi had annexation design over the state.It was only after the full indian invasion of kashmir that the pak army-militias came to the aid of the kashmiris.
(Quoted by Rajendera Sareen in his book Pakistan: The India factor, New Delhi, 1948, p-221) Government of India in order to justify their invasion on State of Jammu Kashmir launched a propaganda that there was no Poonch rebellion but that 1,00,000 ferocious Tribesman had invaded Kashmir at the instigation of Pakistan Government who looted and killed everyone coming in their way; and that they had been imparted training and supplied transport facilities by Pakistan Army.
1.Dogra regime go on mass killing spree of muslim in jammu
2.Indian army assisted by Hindu and Sikh extremists —— both local and those imported from the East Punjab help dogra forces.
3.Uprising in kashmir with poonchis-mirpuris soldiers taking the lead
4.Full invasion by the indian army
5.Followed by pak army-militia help for kashmiris
Now moving onto the instrument of accesion
According to the Indians the original “Article of of Accession” for the state of Kashmir is lost–as if it ever existed. There are serious issues of timing and dates pointed out by various international, Pakistani and Indian authors–The works of Stanley Wolpert and Alistair Lamb stand out in this matter.
Kashmir article of accession was never presented to Pakistan or the UN. It has now been lost, if it ever existed. Even the forged copy has problems with dates The International Commission of Jurists (ICJ), based in Geneva, passed a resolution proclaiming Kashmir’s accession to India as bogus and null and void.
Alastair Lamb (in his book, Kashmir – A disputed legacy 1846-1990) points out that the Instrument of Accession could not have been signed by the Mahrajah on 26th October as he was travelling by road to Jammu (a distance of over 350 Km).
No satisfactory original of the Instrument of Accession has ever been produced in an international forum; a published form has always been shown. Further, the document was not presented to Pakistan or to the UN. In the summer of 1995, the Indian authorities reported the original document as lost or stolen. This sheds further doubt on whether the Mahrajah actually signed the Instrument of Accession.