As recently as March, the Pakistani Taliban, which claimed responsibility for Sunday's attack on Karachi airport, announced a cease-fire with the government. A month later, that cease-fire was over amid accusations by the group that the government had killed militants during the period.
The Pakistani Taliban are seen by many as the most significant threat to Pakistan's internal security. Sunday's attack was the latest high-profile operation carried out by the group, which is accused of being behind the 2007 assassination of former Prime Minister Benazir Bhutto as well the attack on schoolgirl Malala Yousafzai.
So who are the Pakistani Taliban, and what are they fighting for?
In 2007, the Tehrik-e-Taliban Pakistan, as the group is officially known, united dozens of militant groups that operate along Pakistan's border with Afghanistan. They have close links to the Afghan Taliban and coordinate with that group on their activities inside Afghanistan. The Pakistani Taliban also have close links to al-Qaida, a relationship the U.S. calls "symbiotic."
The U.S. placed the Pakistani Taliban on its list of foreign terrorist organizations in September 2010.
At the time of its founding, the Pakistani Taliban said their goal was to attack Western troops in Afghanistan. The group's leadership also said they would engage in "defensive jihad" against Pakistani operations inside the semiautonomous tribal regions in northwest Pakistan. The group wants to enforce Shariah, or Islamic law, in Pakistan.
In recent years, the Pakistani Taliban's influence has spread far beyond the group's traditional power centers of the northwestern region.
That was on display Sunday in the attack on Karachi's airport, the country's largest. The southern port city has a history of violence. As NPR's Dina Temple-Raston reported last year: "The sad truth about Karachi in 2012 was that whatever your religion, business affiliation, or political party, someone was willing to kill you for it."
Most of those deaths were attributed to sectarian violence and score-settling. But Dina noted in her reporting, "For the first time, local extremist groups are joining forces in a coordinated way with the Tehrik-e-Taliban, also known as the Pakistani Taliban, or TTP."
Besides the assassination of Bhutto, the attack on Malala and, now, the airport operations, the Pakistan Taliban have claimed responsibility for several attacks. Here are some:
In 2009, the group carried out a suicide attack on a U.S. military base in Khost, Afghanistan, killing seven Americans.
A year later, the group struck the Peshawar airport, killing seven people.
The group's successes have come amid periodic setbacks.
Both those deaths were seen as serious losses for the Pakistani Taliban. The group's current leader is Mullah Fazlullah, a man who rose to prominence in the Swat Valley through his fiery religious radio broadcasts.
Although Pakistan is reeling from the attacks carried out by the group and the mounting civilian casualties, many experts point to the country's backing of militant groups. Here's Pakistani journalist Ahmed Rashid, writing in The New York Review of Books:
"For forty years Pakistan has been backing Islamic extremist groups as part of its expansionist foreign policy in Afghanistan and Central Asia and its efforts to maintain equilibrium with India, its much larger enemy. Now Pakistan is undergoing the worst terrorist backlash in the entire region. Some 50,000 people have died in three separate and continuing insurgencies: one by the Taliban in the northwest, the other in Balochistan by Baloch separatists, and the third in Karachi by several ethnic groups. That sectarian war, involving suicide bombers, massacres, and kidnappings, has gripped the country for a decade."
Rashid notes that the country's military had long used militant groups as a foreign policy tool against India and Afghanistan. And while the West overlooked this for a while, the policy became unacceptable to the U.S. after the attacks of Sept. 11, 2001. But the Pakistani military's insecurity about U.S. intentions in the region, and the rising power of India and Afghan opposition groups, led to "its fateful decision to rearm the Taliban," according to Rashid.
"It believed that the Taliban would provide a form of protection for the Pakistani military against its enemies," Rashid writes. "Instead the revamped Afghan Taliban helped create the Pakistani Taliban and the worst blowback of terrorism in Pakistan's history."