As British officials continued their hunt for Muslim extremists in what they described as their biggest security operations since World War II, another group that used fear and violence for decades - the Irish Republican Army - announced Thursday it was permanently abandoning military operations.
The decision by the IRA - which used assassinations and bombings to pursue its goal of a Northern Ireland free from British rule - is a poignant coda to one era of terrorism. Politically, it also offers a possible break in the standoff between Northern Ireland's Catholics and Protestants that for months has stymied progress toward a peace accord.
The IRA statement directed all units to cease armed activity now and pledged to pursue its aims through politics, a move that some officials and experts said offered the best hope of reaching a lasting political settlement since Catholic-Protestant relations broke down in December.
The IRA said it had invited two independent witnesses, from the Protestant and Catholic churches, to verify that it will put its massive arsenal of guns and explosives beyond use, but it gave no dates for starting or completing the process.
British Prime Minister Tony Blair hailed the announcement as "a step of unparalleled magnitude in the recent history of Northern Ireland."
"This may be the day when finally after all the false dawns and dashed hope, peace replaces war, politics replaces terror on the island of Ireland," Mr. Blair said.
But Northern Ireland's Democratic Unionist Party (DUP), which favors continued union with Britain, reacted more skeptically. Some unionists responded to the IRA pledge by noting that disarmament has for years been a frustrating stop-start process that has yet to provide conclusive proof of the republican movement's commitment to peace.
Jeffrey Donaldson, a member of Parliament form the hardline DUP, said, "We've no indication in this statement of when that will be done, they simply say it will be done as soon as possible," he says. "We don't know whether that means one week, two weeks, six months, a year, so obviously we need to wait and see what happens there."
Elsewhere in mainland Britain, reaction was muted by the sense that the IRA threat has been supplanted by the new menace of Islamist terrorism.
But in some ways the IRA announcement, as it reflects the fits-and-starts weaning from violence of a guerrilla movement, is a product of the rise of Islamist extremism, some experts say.
"This announcement has 9/11 written all over it, because that terrible day changed forever the way Americans, the Irish, the British, many people view freedom-fighter struggles," says John Hulsman, a specialist in European affairs at the Heritage Foundation in Washington.
Before the shock of Sept. 11, 2001, the idea had currency that "one man's terrorist is another man's freedom fighter, but that's not true any more," says Mr. Hulsman, who has focused on the Northern Ireland conflict. "If there's any beneficial side effect to the rise of Muslim extremism it may be the realization that we live in a different time when violent extremism is not acceptable. The IRA and Sinn Fein [the Irish republican movement's political wing] seem to be finally recognizing this."
Hulsman says 9/11 also took its toll on the IRA because it accelerated a distaste for violence that had been growing among the guerrilla army's crucial American supporters. American moral and financial support, centered in the Irish-Catholic community, was key to the movement's survival.
"The terrorist attacks on the US changed Americans' perspective and got things rolling, but the IRA's continuing criminal activities have only dug their hole deeper," Hulsman says. "They've totally estranged themselves from their American supporters, who had been bankrolling Sinn Fein for decades."
Some British observers say it is ironic that the breakthrough has come at a time when most Britons have largely forgotten the bad old days of IRA bombings and have their eye on a very different menace.
The IRA have not killed anyone in mainland Britain for almost a decade. In August 1998, the Real IRA, a splinter group of former Provisional Irish Republican Army members, killed 29 people in Omagh. That was the most killed in any single attack. And when the IRA or its splinter groups, conducted acts of violence, the attacks were normally preceded by a phone tip-off to minimize casualties. [Editor's note: The original version misidentified the group responsible for the Omagh bombing.]
"There was an old terrorism analysts' phrase that the IRA wanted to have a lot of people watching but not a lot of people dead," says Dana Allin, a security expert with the London-based International Institute for Strategic Studies. While there is no question that mass casualties are the goal of the new breed of Islamist terrorism shaking Britain, he says, "this old-style terrorism was always about negotiable questions."
With the focus on Northern Ireland now turning to the prospects for permanent peace, Mr. Allin notes that "the new terrorism is distinguished by a different order of ideology and threat. It doesn't seem to be negotiable."
The IRA announcement, coupled with recent Sinn Fein actions against continuing violent and illegal activities, suggest a movement interested in negotiation and political standing. The IRA recognizes that the "ball is in its court" in terms of next steps, several analysts say, and is signaling that it wants to be back on the political offensive.
"The focus has been on the bad behavior and misdeeds of the IRA, and they seem to want to change that," says Adrian Guelke, a professor of comparative politics at Queen's University in Belfast, Northern Ireland. Northern Ireland's biggest bank robbery in history, committed in December, was attributed to the IRA, while the organization has gained negative attention for its practice of beating and exiling unfaithful members.
The case of Robert McCarthy, an Irish civilian killed in a bar fight by IRA members in January, also received substantial attention in the US when the victim's sisters crossed the Atlantic in their campaign to get the IRA to turn over the killers.
Mr. Guelke says the IRA announcement will "get the ball moving again" between Northern Ireland's Catholics and Protestants, but he does not expect any quick results. The DUP will continue to cast doubt on the statement's failure to mention criminal and paramilitary activity, he says. And in any case, he suggests that it may be three to six months before the Independent Monitoring Commission will be able to confirm the IRA's moves.
"It will probably be a year and a bit before the [Catholic-Protestant coalition]government is back up and running - and that's if everything goes pretty well," he says.
Heritage's Hulsman says what may keep the two sides moving forward is the PR battle they are currently locked in. A combination of factors - a wish to put off the "terrorist" label, demographics that suggest Northern Ireland's Catholics could become the majority in a generation, and Ireland's booming economy - all favor the IRA's move out of violence, he says.
Guelke agrees. "They realized they had to get finally and fully out of the terrorism business - or risk what was liable to become an association with jihadist terrorism," he says.
Major events in the struggle over Northern ireland:
1921: South declares free state. Civil war rages for two years. Northern Protestants remain loyal to Britain.
1937: Irish Free State (26 counties in south and west Ireland) proclaims independence, not recognized by Britain until 12 years later.
1955-62: Sporadic attacks by the Catholic Irish Republican Army against British in Northern Ireland and England.
1968: N. Irish Catholics launch civil rights campaign.
1969: British army sent to Northern Ireland to quell worst clashes in 50 years.
1972: British troops kill 13 Catholic protesters on "Bloody Sunday" in Londonderry.
1972: British government introduces direct rule in N. Ireland.
1979: IRA steps up attacks on prominent Britons.
1981: Ten IRA prisoners starve to death in hunger strike designed to secure political-prisoner status.
1982: N. Ireland assembly elected; boycotted by Catholics.
1984: IRA bomb at British Conservative Party conference kills five.
1985: Anglo-Irish agreement gives Dublin government a consultative voice in N. Ireland.
1994: IRA announces cease-fire, matched by pro-British guerrillas. British officials hold first open meeting with Sinn Fein in more than 70 years.
1996: IRA ends cease-fire; multi-party talks on the future of N. Ireland begin; Sinn Fein is excluded.
1997: Adams and chief negotiator Martin McGuiness win seats in British parliament but decline to take them up. IRA announces "unequivocal" ceasefire. Two Protestant parties quit talks in protest at lack of IRA commitment to hand in its arms.
1998: "Good Friday" peace deal follows marathon talks to end conflict and devolve rule. Elections to a new Northern Ireland Assembly held; Protestant Ulster Unionist Party (UUP) leader David Trimble elected first minister designate. Car bomb in Omagh, N. Ireland, kills 29 in worst single attack in nearly 30 years of violence. IRA splinter group claims responsibility.
1999: Province gets own government in which Catholics and Protestants share power, ending 27 years of rule from London.
2001: Trimble resigns over IRA failure to disarm; reelected when IRA puts some arms beyond use.
2003: Assembly elections boost hard-liners.
2004: Blair and Ahern open summit to reach a deal. IRA guerrillas later refuse the photographing of their disarmament, the last sticking point in the drive for a political settlement.
2005: Trimble resigns as leader of the UUP after poor results in Britain's election. Hard-line Democratic Unionist Party (DUP) of Ian Paisley surges ahead. IRA pledges to dump arms, commits to political solution in N. Ireland.