The United States and the Taliban signed a historic peace accord Saturday, the first step in a fragile process that could end America’s longest war in Afghanistan begun after the Sept. 11, 2001 terror attacks.

The deal involves several interim steps, including a prisoner swap between the Taliban and Afghanistan’s government, negotiations for reconciliation among the various parties inside the war-weary country, and the drawdown of American troops from 13,000 to about 8,600 in the next few months.

The Taliban must also continue the decrease in recent violence inside Afghanistan and refuse to harbor terrorists, like those from Al-Qaeda that pulled off the 2001 attacks.

But if the benchmarks are met and the peace holds, U.S troops could completely withdraw from Afghanistan within 14 months, meeting another of Trump’s 2016 campaign promises.

The actual agreement was signed in Doha, Qatar with Secretary of State Mike Pompeo presiding. Defense Secretary George Esper, meanwhile, arrived in Kabul to cheer on the deal while sounding cautious optimism.

“This is a hopeful moment, but it is only the beginning. The road ahead will not be easy,” Esper said, calling on the Afghan parties to exhibit patience and compromise in the negotiations ahead.

Esper added the United States would “not hesitate to nullify the agreement” if the Taliban failed to honor its commitments, including ending safe harbor for any terrorist groups.

In Washington, President Trump urged all sides to try to make good on the deal, which would deliver on his 2016 campaign promise to end the Afghan war.

“If the Taliban and the government of Afghanistan live up to these commitments, we will have a powerful path forward to end the war in Afghanistan and bring our troops home,” Trump said hours before the deal was signed.

The president said a key step in gauging success would be the reconciliation negotiations. "Ultimately, it will be up to the people of Afghanistan to work out their future. We, therefore, urge the Afghan people to seize this opportunity for peace and a new future for their country,” he said.