NEW DELHI (AP) — India and Pakistan’s latest military conflict has expanded, days after India carried out airstrikes in Pakistan that followed an attack by gunmen on tourists in India-controlled Kashmir last month.

The two nuclear-armed rivals have exchanged artillery shells, gunfire, missiles and drones, killing civilians on both sides and raising concerns of a wider war.

The fresh round of confrontation is yet another escalation of a decades-long conflict over the disputed Kashmir region that began after a bloody partition of India in 1947.

Here’s a look at the troubled legacy of Partition that has dictated the future course of India-Pakistan relations:

Partition created two new nations

In August 1947, Britain divided India, its former colony, into two countries — Hindu-majority India and Muslim-majority Pakistan. The fate of Kashmir — then a princely state — was left undecided.

Excitement over independence was quickly overshadowed by some of the worst bloodletting that left up to 1 million people dead as gangs of Hindus and Muslims slaughtered each other.

Creating two independent nations also tore apart millions of Hindu and Muslim families in one of the world’s largest peacetime migrations.

Many fled their homes and lost their property, never imagining that they would not be able to return.

At least 15 million people were displaced.

Both nations lay claim over Kashmir

Within months, both India and Pakistan laid claim over Kashmir, a Muslim-majority region.

Kashmir’s Hindu ruler wanted to stay independent, but local armed uprisings flared in various parts of Kashmir, along with a raid by tribesmen from Pakistan. It forced the monarch to seek help from India, which offered military assistance on condition that the kingdom link itself to India.

The Indian military entered the region soon after, with the tribal raid spiraling into the first of two wars between India and Pakistan over Kashmir. That war ended in 1948 with a U.N.-brokered ceasefire. Kashmir was divided between the two young nations by the heavily militarized Ceasefire Line that was later named Line of Control.