It is not easy or overnight as it seems to be.

It is the culmination of the events and decisions which happened in the last 6 years.

Allow me to put them one by one.

1. In 2014, Modi wins. Shortly after that, Ram Madhav(BJP National Secretary) told the former Pakistan minister in a meeting that Pakistan should forget about 370 and 35A. That Pakistani minister revealed this in a Pakistani show on August 4, 2019.

2. In 2014, India asks UN body which is in India since the 1950s to look at Kashmir's issue, to leave telling that Kashmir is the internal matter of India.

3. In 2015, BJP forms an alliance with PDP in JnK despite ideological differences. Every political analyst was surprised by this. PDP could have gone with the National conference of Omar Abdullah also, but they got assurances from BJP.

4. In 2016, Pakistan's economy started to go for a tailspin. Their journey to bankruptcy starts.

5. In the following years, BJP tries to coax PDP on 370. PDP refuses it every time.

6. Donald Trump becomes US president in 2017. In his presidential campaign, he said to pull out the USA from Afghanistan leaving it to deal with the Taliban which is backed by Pakistan. Red flags for India and BJP.

7. BJP tactfully worsens the relations with PDP, tarnishing their image in front of separatists. This was done over time to weaken the support of the Kashmiris and National conference for Mehbooba.

8. In June 2018, BJP pulls out their support from PDP. Mehbooba Mufti resigns as CM as the National Conference of Omar Abdullah was against them due to their association with BJP.

9. Satyapal Malik gets appointed as governor of JnK in August 2018.

10. The economy of Pakistan comes into shambles. Imran Khan, an inexperienced politician, becomes PM of Pakistan in 2018.

11. In August 2018, when the Election commission delays in giving new dates for State Elections, PDP, Congress, and National conference finally form an alliance to make government in Jammu and Kashmir. They send the paper via fax to Governor.

12. Governor, using article 356, puts President Rule in JnK saying that he didn't receive the fax from PDP to form govt as his 'FAX MACHINE WAS NOT WORKING'. So BJP remains successful in keeping away separatists people from taking power in Kashmir.

13. Article 356 of the Constitution moves the power of assembly of the state to Governor. But BJP is not sure whether Article 356 can supersede Article 370. The question remains on the validity of the decision taken by the Governor under President Rule in JnK.

14. To test this, in March 2019, BJP brings SC/ST amendment Bill for JnK. JnK governor approves it. The only person who noticed this trick was Omar Abdullah who cried on Twitter regarding this.

15. This bill passes the validity test from the Supreme Court. This confirms that Govt of India can now take decisions for JnK on the approval of Governor of JnK. It clears the path for removal of 370 and 35A as permission of JnK govt is required(Governor in this case).

16. Intelligence agencies(read BJP) ask Election commission not to conduct State elections of JnK along with General Elections 2019. Separatists oppose this as this kept the state further under President Rule.

17. Pakistan's Economy is staring at the bottom now. They don't have the required resources to go for conventional aggression with India anymore. Further, the economic and diplomatic costs of Balakot for Pakistan become too high. This is followed by Modi again becoming PM in May 2019.

18. Amarnath Yatra starts on July 1. Terrorist infiltration increases a little along the border with significant ceasefire violations.

19. Trump along with Imran Khan, on July 22, makes a strategic blunder saying that Modi asked him to mediate on Kashmir. This was enough for India to know that a trade-off is happening between Pakistan and the USA where Pakistan will help the USA in Afghanistan if the USA helps Pakistan in Kashmir. So one more reason to act on Article 370.

20. The government decides to test the opposition strength in Rajya Sabha by introducing bills like Triple Talaq, RTI Amendment, NMC, Motor Vehicle Amendment, etc. Point to be noted that NDA doesn’t have a majority in Rajya Sabha. So, they manage to break into the camps of opposition and clear bills in Rajya Sabha.

21. On July 25, the Government extends the Parliament session till August 7 to pass pending bills. Amit Shah and Modi have made up their minds on Article 370 and 35A now.

22. Parallelly China, which is concerned with Ladakh, gets tied up with Hongkong protests which are going on till date. So, a possibility occurs that China won't do much as it has to fix Internal issues first.

23. On 2nd August, the USA decides to pull out of Afghanistan by making a deal with the Taliban. Pakistan, using this opportunity, increases attacks on the border in Kashmir to send more terrorists to attack Amarnath Yatra and other places.

24. Parallelly, Pakistan BAT soldiers get killed by the Indian army, and a huge cache of Pakistani weapons is found. This was the final indication to India that now Pakistan will do more terrorist attacks, and the USA will not intervene because of Afghanistan.

25. India locks down JnK, sends troops, and prepares to remove 370 and 35A.

26. On August 5, the President of India signs an order to make 370 and 35A useless and integrating Kashmir with India.

27. Home Minister Amit Shah, presented the bill to bifurcate JnK in Rajya sabha first despite BJP not having a majority. He wanted to take the opposition by surprise and divide them on this issue. Rajya Sabha passes it, followed by Lok Sabha.

28. It ends. A historical mistake done by India gets rectified.

So, here ends the short story of the overnight decision. I hope you enjoyed it.

As you can see that it was not an easy decision at all. Years of preparation went into it to make it successful.

Those questioning the timing and way of this decision and giving lectures on Morality and the Constitution, please understand that India might not get this opportunity to do away with 370 again. So instead of spreading hate in society, start working for the country and become more Indian than your current self.

Thanks for reading.

Edit 1: Thanks for so much support and appreciation. I would like to make one thing clear that this answer is not just from my efforts but from the other people also whose views I have read on Social Media. So, kudos to everyone.

Edit 2: On my interactions with so many people in the comment section, I realized that I have missed mentioning a paramount thing in my answer. And that is the way in which our Prime Minister Shri Narendra Modi has handled the Diplomacy in the last 6 years. Today, the UN and every country except China/Pakistan are either supporting us or are silent on this matter. This would not have been possible without the able leadership of our PM and the brilliant hard work of the Late Madam Sushma Swaraj as a Foreign affairs minister in the years of 2014–19. India was blessed to have her as our Foreign Minister.

Edit 3: When I wrote this answer in August 2019, I mentioned in point number 19 that Trump's statement on Kashmir Mediation is one of the steps which led to Article 370 removal. And today, on 19th Feb 2020, I have been proved to be right with this article in the Economic Times of India.

President Trump’s offer on Kashmir may have expedited scrapping of Article 370: CRS

Footnotes