COLOMBIAN VOTERS stunned their government last month by rejecting a painstakingly negotiated peace accord with the FARC guerrilla movement, potentially reopening a 52-year-old war that has killed some 225,000 people. Complacency was part of the problem: Sixty percent of the electorate failed to turn out for the referendum, and the “no” vote was concentrated in cities far from the rural areas where the FARC has wreaked havoc. But many Colombians had serious objections to the pact, which would have provided amnesty for the insurrection’s 7,000 remaining fighters and allowed their leaders to join the political system.

Now President Juan Manuel Santos, who was awarded the Nobel Peace Prize shortly after the negative vote, has produced a new and amended accord that he says addresses most of the critics’ concerns. Intensive talks between the government and opponents had produced a list of 57 issues; the president says 56 were addressed in the new deal with the FARC. It’s likely that some of the accord’s toughest adversaries will remain unsatisfied. But Mr. Santos would be right to move forward with the new agreement by seeking its ratification by Colombia’s Congress.

The implementation of the deal could end the last Cold War-era conflict in Latin America; the FARC was originally a Cuban-inspired Marxist movement that later took up drug trafficking. It could open Colombia’s vast hinterlands — the country is larger than Texas, Louisiana and New Mexico combined — to investment and development, and provide alternatives to cocaine production and trafficking. It would also represent a foreign policy success for the United States, which beginning in the 1990s helped build and professionalize Colombia’s military so that it could defeat the FARC on the battlefield.

If that bipartisan policy has become more controversial in Washington, it is because Mr. Santos’s predecessor Álvaro Uribe, who led the fight against the FARC from 2002 to 2010, has been critical of the peace settlement. Mr. Uribe in particular objected to the failure of the accord to provide for imprisonment of FARC leaders guilty of war crimes and its allowance of their conversion into political officeholders.

The revised accord only partly addresses those concerns. Militants convicted of crimes by special tribunals would be confined to specified areas for determined periods; judges could effectively make it impossible for them to travel to the capital. The FARC would also be required to disclose its assets so that they may be used for reparations to victims. But the movement would still be guaranteed a certain number of seats in Congress, and its leaders would not be explicitly banned from holding them. The FARC argues that this is essential for its conversion to a peaceful democratic political party; in that there is some logic.

Mr. Uribe has not yet taken a position on the new accord, but he appears to be in agreement with Mr. Santos that its fate should be decided by Colombia’s Congress, not another referendum. If it is approved, the U.S. Congress should be ready to support it, by appropriating the $100 million in additional aid requested by President Obama. Colombia is finally on the verge of ending one of the hemisphere’s most vicious and destabilizing conflicts; the United States, which did so much to make that possible, should help secure what ought to be seen as a clean foreign policy victory.