DUBLIN — Nowhere outside the United States is the passing of Sen. Edward Kennedy being mourned as much as in Ireland, the country from where his ancestors emigrated during the potato famine of the 19th century and to which he helped bring peace in recent years.

President Mary McAleese said he would be remembered as a "hugely important friend to the country during very difficult times," and Prime Minister Brian Cowen commented that Ireland had lost a true friend who "worked valiantly for the cause of peace on this island."

The sentiments are not overblown. The Massachusetts senator was for four decades the Irish government's staunchest ally on Capitol Hill. He first became involved in Ireland in 1971 when he told the U.S. Senate that, "Ulster is becoming Britain's Vietnam" and that British troops should be withdrawn.

Such statements aroused deep resentment in the British establishment. When as a reporter in London I asked Lord Hailsham, then-Lord Chancellor, what effect such interventions by Irish Americans like Sen. Kennedy would have on British policy on Ireland, he retorted angrily: "Those Roman Catholic bastards, how dare they interfere!"

Kennedy grew uneasy, however, about being associated with Irish-American groups supporting violence to achieve the same goal of a united Ireland. In 1972 he sought out John Hume in Derry for advice. As leader of the moderate nationalist party, the Social Democratic and Labour Party, in Northern Ireland, Hume was a prominent critic of pro-IRA sentiment among Irish Americans. The senator was so impressed with the former Derry schoolteacher's impassioned argument for constitutional reform that from then on he aligned himself with Hume on Irish issues.

He joined forces with Speaker of the House Tip O'Neill, Sen. Daniel Patrick Moynihan of New York state, and Governor Hugh Carey of New York to form a group known as the Four Horsemen, who appealed to Americans every St. Patrick's Day to renounce any action that promoted violence. The government in Dublin recognized Kennedy's value as a counterweight to the influence in the United States of groups sympathetic to the outlawed IRA, such as Irish Northern Aid (Noraid).

He became a close ally of Sean Donlon, who as Irish ambassador to Washington from 1978, took on these groups in a bitter struggle for influence. When Charles Haughey became Irish prime minister in 1979, and made a move to replace Donlon in order to placate the more militant Irish-Americans, Kennedy and the other Horsemen got Haughey to change his mind. The Massachusetts senator later helped persuade President Ronald Reagan to lean on British Prime Minister Margaret Thatcher to sign up to the landmark 1985 Anglo-Irish Agreement, giving the Dublin government a say in Northern Ireland affairs for the first time.

When Bill Clinton was elected president in 1992, Kennedy persuaded him to appoint his sister Jean Kennedy Smith as ambassador to Ireland. Kennedy then made another crucial intervention with the White House that influenced the course of Irish history. Clinton had made a qualified promise to grant a U.S. visa to Gerry Adams, leader of the IRA's political wing, Sinn Fein, up to then banned from the United States as a spokesman for a terror group.

In December 1993 a group of influential Irish-American businessmen organized by New York publisher Niall O'Dowd sought a visa to allow Adams to promote his plans for peace at a conference in New York. Kennedy was at first opposed. But on a visit to Dublin his sister brought him to meet the then prime minister Albert Reynolds, who said that "I think you should go for it because I think he (Adams) wants peace."

Kennedy was not totally convinced, but shortly afterward, at the funeral of Tip O'Neill in Boston, he got the same advice from John Hume. Kennedy then rallied fellow senators, including George Mitchell, to put pressure on Clinton to grant the visa. His intervention provided essential political cover for the president, who was inclined to take the risk but was facing strong opposition from the U.S. State Department, the FBI and the British Embassy.

The British were furious when the visa was authorized. "See what the Brits are saying about me?" said Clinton when Kennedy called to thank him. "Don't worry about it," the senator replied. "That's what the Brits have been saying about the Kennedys for years." The IRA, convinced partly by Clinton's decision of the political benefits of ending violence, declared a cease-fire six months later. The decision on the visa, in the opinion of Gerry Adams, brought forward the IRA cease-fire, and subsequent loyalist paramilitary cease-fires, by about a year, saving many lives.

Jonathan Powell, who as a Washington-based British diplomat opposed the visa vigorously, wrote in his 2008 book "Great Hatred, Little Room" that in retrospect "Clinton was clearly right in the decision he made." After the cease-fire Kennedy made a point of welcoming Northern Ireland politicians from both traditions to his Capitol Hill office as a power-sharing deal was worked out. In March this year Kennedy's role in the Irish peace process was also recognised in London, when the Labour Government granted him an honorary knighthood for "services to the British-American relationship and to Northern Ireland."