The spark for the latest round of escalation between India and Pakistan, the most expansive fighting between the enemies in decades, was a terrorist slaughter of civilians in Kashmir last month.

A group of attackers managed to puncture the semblance of calm that the Indian government had been projecting on its side of the troubled Kashmir region, long the flashpoint of dispute between the two neighbors. The attackers came out of the woods in a scenic picnic spot and killed 26 men. The men, almost all of them Hindu, were identified by their religion, and many of them were killed in front of their wives and families, according to witness accounts.

A little known group called the Resistance Front claimed responsibility. The Indian government said that the group was a front for a broader terrorist apparatus that has operated out of Pakistan, and it announced a series of strikes against Pakistan that has now broken into military conflict. Pakistan has rejected those claims.

Here is what we know about the groups that India said it had targeted in its military strikes.

What are the two main groups India targeted?

Lashkar-e-Taiba, which was founded in the 1980s, has long been suspected of masterminding from Pakistan some of the worst terrorist attacks in India. It was added to the U.N. sanctions list in 2005.

One of the deadliest attacks the group orchestrated was the 2008 slaughter in Mumbai, India’s financial hub, during which more than 160 people were killed. Nearly a dozen gunmen arrived on boats and waged a day of carnage, including taking hostages at a major hotel. One of the attackers was captured alive, and much of the account of the attack’s ties to Pakistan came from his confessions. He was sentenced in India in 2010 and executed in 2012.

Pakistan has confirmed Lashkar-e-Taiba links to past violence in India but says that the group was outlawed and disbanded long ago. The group’s founder, Hafiz Saeed, is free despite brief periods of detention, and Indian officials say that the group continues its activities through multiple cover organization and offshoots, such as the Resistance Front.