India launched an airstrike on a target within Pakistan yesterday, the most serious escalation in hostilities between the two countries in decades.
According to Indian officials, the strike's target was the training camp of a Pakistan-based militant group that had claimed responsibility for a massive suicide bombing in Indian-controlled Kashmir on February 14.
The nuclear-armed neighbours have a long history of animosity. The main, ongoing source of conflict is Kashmir, a Himalayan border region whose status has been contested ever since India gained independence and Pakistan was created in the partition of British India.
Since then, the two countries have fought three brief wars - in 1947, 1965 and 1971 - as well as a smaller conflict in 1999. Over the last two decades, there have also been numerous attempts at rapprochement: At one point secret talks reportedly neared a final resolution on Kashmir.
Now, with the February 14 attack and India's retaliatory strike, tensions are once again on the rise.
For India, the Kashmir attack is part of a longer pattern in which Pakistan's intelligence services have fostered and guided militant groups that carry out deadly attacks throughout India.
Pakistan views its far larger neighbor as an occupying power in Kashmir that also seeks to undermine Pakistan's own stability. Pakistan denies supporting terrorism but says it gives political and moral support to Kashmiri "freedom fighters."
Here is a selection of recent highs and lows - though mostly lows - in their tense relationship.
1989: The insurgency in Kashmir begins
The dispute over Kashmir is as old as India and Pakistan. India controls the larger and more developed chunk of the Himalayan region, which forms its only Muslim-majority state. In 1987, legislative elections were held in Indian-controlled Kashmir, but Kashmiri Muslims protested that the polls were rigged. Two years later, an armed insurgency erupted in the region, along with mass protests. The militancy against Indian rule has continued, with ebbs and flows, ever since. More than 70,000 people have been killed, according to human rights groups.
1999: A bus trip raises hopes for reconciliation
In 1998, India and Pakistan both tested nuclear devices, marking a fundamental shift in the strategic balance in South Asia. The next year, Indian Prime Minister Atal Bihari Vajpayee travelled by bus to Pakistan across the only official border opening in a gesture of friendship. He and Pakistani Prime Minister Nawaz Sharif pledged to resolve their differences through dialogue.
1999: The Kargil conflict breaks out
Before the year was out, hopes for reconciliation were dashed. After months of cross-border firing in the mountainous Kargil region of Kashmir, the fighting escalated dangerously, with infiltrators from the Pakistani side crossing into high-altitude security posts in India. This time, the spectre of nuclear war hung over the dispute. A meeting between Sharif and US President Bill Clinton in Washington helped end the fighting, and Pakistan withdrew back to the Line of Control, but mutual hostility remained intense.
2001: Gunmen storm India's Parliament
In December, five militants attacked India's Parliament in the heart of New Delhi, killing nine people before the attackers were shot dead. The brazenness of the attack - in the most secure area of the capital, on a target symbolising Indian democracy - left India shaken and enraged. India blamed the attack on two Pakistan-based militant groups, Lashkar-e-Taiba and Jaish-e-Muhammad, and accused the Pakistani intelligence service of being behind the operation. India massed hundreds of thousands of troops at the border with Pakistan and kept them there for the better part of a year.
2004: Leaders launch a peace initiative
After the attack on India's Parliament, the relationship between India and Pakistan entered a deep freeze. But by late 2003, the atmosphere began to thaw: Top diplomats returned to Islamabad and New Delhi, and transportation links between the two countries were reinstated. Most promising of all: An agreement by Indian Prime Minister Vajpayee and Pakistani President Pervez Musharraf to open talks on all issues, including Kashmir. The talks continued for three years.
2008: Terrorists strike Mumbai
In November, a team of 10 attackers approached India's financial capital by sea and targeted a railway station, two luxury hotels, a renowned cafe and a Jewish community centre. By the time their three-day killing spree was over, more than 160 people were dead. India presented Pakistan with a dossier showing that the attack was planned and carried out by Lashkar-e-Taiba. India also said Pakistan's spy agency helped orchestrate the attack. Last year, devotees of Lashkar's former leader ran for Parliament in Pakistan's elections.
2016: India launches "surgical strikes" across the line dividing Kashmir
After militants belonging to a Pakistan-based militant group stormed an Indian army base in Kashmir, killing 19 soldiers, Indian Prime Minister Narendra Modi promised to respond. India announced that it had launched "surgical strikes" in Pakistani-controlled Kashmir - commando raids that crossed the Line of Control. Indian experts said similar raids had been conducted before but never made public. Pakistan said no such incursions took place.
2019: Pakistan-based group carries out deadliest attack of 30-year Kashmir insurgency - and India retaliates
On February 14, a suicide attacker rammed an explosives-laden SUV into a convoy of Indian paramilitary police, killing 40. The attacker was a local Kashmiri teenager who had joined Jaish-e-Muhammad, a Pakistan-based militant group.
Indian Prime Minister Narendra Modi vowed to "avenge every tear" that was shed in the wake of the bombing. Pakistani Prime Minister Imran Khan said the country would take action against anyone involved in the attack "if evidence is found." He also vowed to retaliate if India responded to the attack with military action against Pakistani targets.
But India did not heed Khan's warning. In the most serious escalation between the two countries in two decades, Indian fighter jets crossed the Line of Control, and hit a target that, according to India, was a training camp used by Jaish-e-Muhammad. India called its strike a "non-military strike," as it was not aimed at Pakistani military targets, and said it was taking "pre-emptive" action against Jaish-e-Muhammad.