Till then, the US would not believe India's contention that terrorism is harboured, nurtured and encouraged by Pakistan as a tool of its diplomacy and that the country was using Afghanistan, then ruled by its proxy Taliban, as a backyard of the nursery of terror.
Before September 11, 2001, India had borne a lot of brunt of terror exported by Pakistan for over two decades, first in Punjab and then in Jammu and Kashmir. But whenever Indian leaders told the US leadership about it, they would dismiss it as a "law and order" problem.
No amount of evidence would convince Washington that it was not a "law and order" problem but pure terrorism, sponsored by Pakistan to destabilize India.
However, when it started investigation into the 9/11 attacks and found links that led to Pakistan, through Afghanistan, the US perspective changed forever.
It took cognizance of the fact that terrorism was being nurtured in Pakistan and issued stern warnings to the then General Pervez Musharraf-led nation to wind up all such activities or Pakistan would be "bombed to stone age".
A cunning Musharraf immediately changed colours -- from an organizer of terror, he pretended to join the war against terror.
This was clearly to escape the American wrath, which was then limited to Afghanistan, where the US-led international forces began a military campaign and removed Taliban from power. That campaign continues even to this day.
"The 9/11 was an unfortunate development but a wakeup call for the US... It brought terrorism to the doorstep of its mainland... After these attacks, the US has not and will not be the same again," Vishnu Prakash, a retired IFS officer who last served as Indian High Commissioner to Canada, told IANS on Wednesday.
The attacks led the US to launch a war against terrorism in Afghanistan, which was going to cost the country's exchequer $5.9 trillion by 2030, according to some rough estimates, added Prakash, who also served as the Spokesperson of External Affairs Ministry in Delhi.
Prior to the attacks in its heartland, the US believed that such activities were confined to South Asia and could not reach its shores, thousands of miles away.
Prakash noted that the US always believed that the two oceans surrounding it made it impregnable but "its belief of being secure was shattered (by the 9/11 attacks)."
Even after those ghastly attacks, the US has not gone after terrorists of all hues and continues to have double standards.
While it continues to target Al Qaeda, it has been engaging with the terror networks affiliate, the Taliban, even till a few days back, before President Donald Trump called off the talks with the Islamist outfit following continued attacks by it on the American forces in Afghanistan.
The US also has not done enough towards adoption of an Indian proposal for Comprehensive Convention on International Terrorism (CCIT) pending at the UN for over two decades.
"Even today, the CCIT proposal is hanging fire," Prakash pointed out.
The CCIT, which proposes to make it incumbent on all UN member countries to deny its soil to be used for terrorism, is held up because of lack of consensus on the "definition of terrorism".