His presence was generally regarded as an opportunity to move toward a rapprochement between neighbors whose relations have been rocky for as long as anyone can remember.
The effort appeared to take on new significance as Washington signaled it was taking a harder line in its efforts to stamp out the threat of international terrorism from Al-Qaeda and other militants in Pakistan's tribal belt bordering Afghanistan.
In the Pakistani capital for this week's inauguration, Karzai and Zardari vowed to enhance cooperation and indicated they agreed on how to battle insurgents in their border regions.
Careful observers in the region cite strong indications that the political will for rapprochement exists in both Islamabad and Kabul. But they also question whether support within Pakistan's civilian government is sufficient, since it's unclear whether the country's powerful military shares that view.
Ahmed Rashid, a Pakistan-based journalist who has covered the region for three decades and written a number of books on militancy and state building in South and Central Asia, said President Zardari's biggest "battles" are not with his Afghan counterpart -- and won't be won overnight.
He said Zardari "will have to fight with the military, with the intelligence services, to try and change the Afghan policy rather than any kind of tensions with Karzai."
He noted that Zardari's late wife, former Pakistani Prime Minister Benazir Bhutto, struck up a good rapport with Karzai shortly before she was assassinated last year, and said the new president has now followed suit.
Closing A Haven
Kabul, Washington, and NATO blame Taliban and Al-Qaeda sanctuaries in tribal areas for much of the violence in Afghanistan. The United States has recently stepped up attacks against Taliban and Al-Qaeda elements inside Pakistan.
Hundreds of militants, soldiers, and civilians have been killed in recent months in fighting between Pakistani security forces and Islamist militants, generally identified as Taliban, in the Federally Administered Tribal Areas (FATA) and the Northwest Frontier Province.
"There is still a lot of frustration by NATO and the Americans regarding Pakistan," Rashid said ahead of the report that U.S. President George W. Bush gave a green light in July to cross-border operations. "There still seems to be no indication about Pakistan moving against the Afghan Taliban leadership, some of which is living in [the southwestern Pakistani province] of Baluchistan. I think [that] until we start seeing the Pakistanis wrapping [up] some of the Afghan Taliban leadership, I don't think there is really going to be a major shift on the ground."
International media had indicated recently that the Pakistani military leadership was in broad agreement with Washington on pushing for a more robust effort to eliminate militant sanctuaries on its soil.
"We are working with Pakistan in a number of areas, and I do believe that Islamabad appreciates the magnitude of the threat from the tribal areas, particularly considering the uptick in suicide bombings directed at Pakistani targets," U.S. Defense Secretary Robert Gates told the House of Representatives' Armed Services Committee on September 10. "During this time of political turmoil in Pakistan, it is especially critical that we maintain a strong and positive relationship with the government, since any deterioration would be a setback for both Pakistan and Afghanistan. The war on terror started in this region; it must end there."
But the report of U.S. presidential approval for ground assaults on Pakistani soil are almost certain to put a strain on Pakistan's cooperation with international forces in Afghanistan to combat terrorism.
Humayun Khan, a former Pakistani diplomat, told RFE/RL from Peshawar this week that the situation in the lawless FATA had become Pakistan's "first priority."
Khan said Karzai was invited to Zardari's inauguration to demonstrate Islamabad's new commitment to tackling the situation in the tribal regions.
"This was needed because our Afghan brothers and the Americans had long suspected that Pakistan was not doing enough to stop [militant] infiltration into Afghanistan," Khan said.
If At First You Don't Succeed...
Khan stressed that ethnic Pashtuns live on both sides of the Afghan-Pakistani border and future cooperation between the two countries could contribute significantly to stability in that area, which has been devastated by three decades of war and violence.
Khan argued that violence in the past two years, in particular, has forced Pakistan's political leaders to conclude that they cannot live under militant extremists.
It's a conclusion that Afghan's post-9/11 leadership reached a long time ago.
"Both Pakistan and Afghanistan think that such people -- [religious] extremists -- should not dominate our countries," Khan said. "I think both Pakistan and Afghanistan want to control such elements."
But critics in Afghanistan and elsewhere have questioned Islamabad's determination, as well as its motives. Critics accuse Pakistan of using extremist militants as a tool to steer events inside Afghanistan. They suggest Pakistani authorities might simply be backing away from those elements as Islamabad's influence wanes and as international pressure on Pakistan mounts.
Ahmad Saeedi, a former Afghan diplomat turned analyst who is based in Kabul, suggested to RFE/RL that such factors had been weighing heavily on Islamabad to change its strategy.
"Pakistan is now known for supporting terrorists in the region and being involved in other troubles," Saeedi said. "The world now knows about this, and [Pakistan] can no longer play a dominant role in Afghanistan."
Pakistani Foreign Minister Shah Mehmood Qureshi announced to reporters on September 9 that a joint Afghanistan-Pakistan peace assembly, or jirga, would be held in Islamabad in October. The two sides held a similar event last year in Kabul, but a follow-up meeting in Islamabad never materialized as relations between the two sides soured.
Khan maintained that a process of dialogue and consensus building remains the only option for Afghanistan and Pakistan to improve relations.
"I believe that the real solution is in reconciliation, consultation, and dialogue," Khan said. "I hope that this new jirga will be convened to achieve such objectives."
EYE OF A STORM: Afghan officials first suggested that insurgents or terrorists were crossing the border from Pakistan in 2003. Relations have run hot and cold ever since. But the roots of the problem go back much further.