Everybody benefits from a united island.

As a sectarian riot raged in Dublin last month, the same question was likely heard in every Irish pub: Do we really need these Northern shenanigans?

Even the most ardent supporters of a united Ireland must have cringed when they heard about the donnybrook, sparked by opposition to a march planned by Protestants from Northern Ireland. But the Dublin riot proved that as hard as residents of the Irish Republic try to ignore them, Northerners are never going to go away. In fact, they could become more than just neighbors some day.

On St. Patrick's Day, 2005, the five McCartney sisters—whose brother, a Catholic, was murdered outside a Belfast pub by IRA men—met with President Bush after taking a stand against the Irish Republican Army. The condemnation that followed Robert McCartney's murder and the IRA's alleged $50 million Belfast bank heist led to a stunning declaration last July: The IRA's armed rebellion was over at last. The International Monitoring Commission says the IRA has now finally disarmed and no longer poses a terrorist threat.

As the IRA faded from the scene, Ulster's nationalist leaders pushed their cherished dream of a united Ireland. Several Catholic town councils cast symbolic votes in support of Irish unity. The British army, to the joy of Catholics and the agony of Protestants, began a rapid, dramatic military withdrawal. A united, independent Ireland, at least in theory, seems closer now than ever.

The Catholic portion of the Northern Ireland population keeps growing, from just 37 percent three decades ago to about 45 percent now. Catholic birth rates have historically been higher than Protestants', whose middle-class kids tend to leave for college on the British mainland, never to return. Protestants, whose ghettos are littered with abandoned homes, are expected to become the minority one day, possibly within a generation.

Many moderate Catholics who never supported the IRA want the six Northern counties to join the Irish Republic. That helps to explain Sinn Fein's spectacular growth since it signed the historic Good Friday Agreement in 1998. Under the accord, Northern Ireland can leave the United Kingdom and join Eire only if a majority supports the move.

While Protestants fear abandonment by the British, Catholics know the Irish aren't yearning for reunion. Ulster is a troubled region that nobody wants—not the folks on the other side of the Irish Sea and not the Irish, either, if it means higher taxes.

Before Ireland's 1921 partition, London was ready to free the entire island. Protestants in the booming industrial northeast, fearing domination by backward Catholic farmers, took up arms. The threat of war led to the gerrymandering of a majority Protestant province. The new Irish government, after defeating the anti-partition IRA in the Irish Civil War, quietly abandoned the North.

After Northern Catholics endured a half-century of discrimination, the "Troubles" erupted in 1969. The British considered granting Northern Ireland its independence, according to recently declassified official documents. The Irish, meanwhile, were praying that the British would not withdraw. According to declassified Irish papers, sending in Irish troops would happen only if fighting became so bad that "intervention could not make matters worse."

To spur along the peace process, both nations made their lack of interest in Northern Ireland official. With the Downing Street Declaration of 1993, the United Kingdom bluntly announced that it had no "selfish strategic or economic interest in Northern Ireland." The Irish, with their overwhelming support for the Good Friday Agreement, relinquished their constitutional claim to Ulster.