When the masterminds behind the terror attacks on the United States in 2001 were discovered hiding in Afghanistan, the U.S. sent thousands of troops to hunt them down - and asked Pakistan to help. But Pakistan has its own interests in the region and that has meant for a troublesome alliance.
Few things have exemplified or strained the tenuous relationship between the U.S. and Pakistan more than what happened earlier this year in Abbottabad - the U.S. commando raid that killed Osama bin Laden.
It raised questions in the U.S. about Pakistan’s friendship, and angered many Pakistanis, upset by America's unilateral action.
But Cameron Munter, the U.S. ambassador to Pakistan, told VOA the two nations must remain united against a common enemy.
"The problem we have here is that we are dealing with ruthless people who are bringing something to Pakistan that Pakistan didn't want, just like America didn't want an attack on 9/11," explained Munter. "Pakistan doesn't want these kinds of terrorists. They're bringing them here and trying to drive us apart. Trying to make this sound as if it is somehow a fight that we shouldn't be in together."
When the United States launched its military campaign in Afghanistan, it inserted itself into a far larger, far messier regional struggle.
Tensions between India and Pakistan dominate the sub-continent. They have fought four wars and countless skirmishes since their creation more than 60 years ago. Both possess nuclear weapons.
Pakistan’s western border with Afghanistan is porous, nearly impossible to control. Ethnic Pastuns live on both sides of a disputed line arbitrarily drawn by a 19th century British statesman.
Maleeha Lodhi, the former Pakistani ambassador to the U.S., says Washington didn’t fully understand the ramifications of sending troops to Afghanistan.
"Well, I think the blowback of 10 years of war in Afghanistan has been devastating for Pakistan," Lodhi said. "It led not just to the prolongation of a war that destabilized the region, but it also led to the defeat of America’s own objectives. Because America was unable to distinguish and therefore separate al-Qaida from the Taliban. Pakistan believes that this war and the way it was fought was pushed into Pakistan’s border region."
Taliban, al-Qaida and other insurgents fled into Pakistan when the U.S. led coalition arrived in 2001.
And after Pakistan sided with the U.S, many of the fighters in those tribal regions decided Pakistan’s military and government were legitimate targets.
That led Pakistan’s military to pursue some insurgents, but not others -- notably the Haqqani network, allied to both the Taliban and al-Qaida.
The U.S. responded with drone attacks on insurgents inside Pakistan, sparking a wave of anti-Americanism. Many Pakistanis feel the U.S. is violating their nation's sovereignty.
Will relationship last?
But Ambassador Munter says for the last 10 years the two nations have stood together and suffered together. And, he says, with that shared experience they should hold together.
"Both countries have shown resilience. I think it is a good sign for our relationship," noted the ambassador. "Both countries have suffered and we honor the sacricies that people have made. But huge challenges remain and we're going to have to stay together in order to face them."
Parties on both sides of the relationship question that, though. Whether it’s in the American Congress where there’s talk of cutting aid or in Pakistan where there’s anger and talk of breaking with America for now the two remain allies.
At the end of the day, though, on both sides, a common analogy is often used: better a difficult marriage, than an ugly divorce.