Former U.S. Gen. David Petraeus said the largely peaceful presidential election in Afghanistan over the weekend is a sign that American military intervention is having a positive impact, but cautioned that more time and patience is needed.

In a Wall Street Journal commentary co-written with Michael O'Hanlon, Petraeus called Saturday's election turnout of 7 million "impressive," and added that the decrease in violent episodes around voting from 500 in 2010 to just 150 this time was "a crucial step for a young democracy seeking to demonstrate that it can peacefully pass power from one leader to another."

But with the ultimate successor to Afghan President Hamid Karzai – either former World Bank official Ashraf Ghani, 2009 presidential runner-up Abdullah Abdullah, or former foreign minister Zalmay Rassoul – not likely to be known until July or August, Petraeus said it is important for Americans "to be patient and realistic as we watch and support this process as it plays out over the spring and summer."

That course, he said, still includes six crucial steps: official certification of the votes and uncovering of possible fraud; identifying the two potential candidates for a runoff and having the third bow out peacefully; printing and distributing ballots for a June runoff election that could see a spike in violent incidents due to the onset of warmer weather; certifying the results of the runoff election; having the losing candidate and his followers concede the loss calmly and without incident; and for the winner to build a multiethnic, inclusive government.

Petraeus said the remaining process will definitely be slow and pocked with mistakes but he believes "there is good reason to be hopeful," that these tasks will be completed successfully.

He cited Ghani's stated willingness to campaign against corruption and Abdullah's endorsement of political reforms ranging from a shift from presidential appointment to direct election of governors and composition of a stronger parliament.

While Petraeus acknowledged that this democratic transition to a new president would not be possible without sacrifices and more than 2,300 U.S. servicemen lost in the war, seeing Afghanistan transform from a failed state to fledgling democracy is worth the time and price.

"That's all right. We can wait," Petraeus and O'Hanlon wrote. "Coalition forces have demonstrated patience and resoluteness for 13 years ... We may not be headed for a classic victory, but with continued commitment, the prospects for an acceptable outcome in Afghanistan look fairly good."

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