In 1947, when the British divided the Asian subcontinent into Muslim-dominated Pakistan and Hindu-dominated India, it set off a bloodbath that left around half a million people dead.
Called "Partition" across the subcontinent, it was a bloody baptism for the two newly independent nations from which the region has not recovered.
More than 50 years after independence, the two neighbors have seen three wars, a dangerous arms escalation and the looming threat of a new nuclear war.
At the heart of the seemingly intractable conflict between the two countries is the Himalayan region of Kashmir, famed for its snowcapped mountains and lush green valleys, a region described by travelers, poets and conquerors through centuries as "paradise on earth."
But after a brutal 12-year insurgency that has claimed more than 60,000 lives, according to human rights groups, and almost daily threats of terrorist attacks and military crackdowns, the paradise is for all purposes lost.
While one part of Kashmir lies in Pakistan and another part in India, the two countries have conflicting claims to the whole that are rooted in religion and history.
The Indian position is that Kashmir belongs to the Indian republic because of the Instrument of Accession signed in October 1947 by the Kashmiri ruler at the time, Maharajah Hari Singh, which handed over the princely state to India.
But because the maharajah was a Hindu ruler of a majority-Muslim kingdom, Pakistan rejected the Instrument of Accession. It maintains numerous U.N. resolutions mean that Kashmiris should be allowed to vote in a plebiscite to decide between India or Pakistan.
For its part, India refers to the Simla Agreement signed by then-Indian Prime Minister Indira Gandhi and Pakistani President Zulfikar Ali Bhutto in 1972, which calls for a bilateral solution to the Kashmir issue.
The Simla Agreement came at the end of the second war between the two countries, which erupted when the Indian military backed what was then the East Pakistani independence movement.
Separated by the Indian subcontinent from the rest of Pakistan and reeling from human rights atrocities that are still under dispute, East Pakistan emerged from the conflict as the newly independent nation of Bangladesh.
Wars of Words
While the Simla Agreement reaffirmed the Line of Control between Pakistan- and India-administered Kashmir that was arrived at after the 1947 war, the violence flared again in 1982 when an insurgency broke out in India-administered Kashmir.
India holds Pakistan responsible for sponsoring militant Islamic groups in India-controlled Kashmir. It says Pakistani madrassas (religious schools) as well as Pakistan-supported training camps in Afghanistan through the 1980s and 1990s have trained recruits from across the Muslim world to operate in Kashmir.
Pakistan insists it only offers the groups moral support and accuses India of denying Muslim-majority Kashmiris the right to national self-determination.
In the summer of 1998, the conflict reached alarming proportions when New Delhi announced it had conducted successful nuclear tests in northwestern India. Weeks later, Pakistan announced that it had conducted five nuclear tests of its own.