Should we be worried about Northern Ireland? As Scotland prepares for a vote on independence later this week, possibly heralding a broader decomposition of the union, nervous glances are being directed toward the United Kingdom's most restive nation.

Gerry Adams, the leader of Sinn Fein, may be warmly remembering the contributions to peace made by Ian Paisley, the arch-unionist who died last week. But Adams has been warning over and over again that the peace process in Northern Ireland is falling apart. The cease-fire that ended (almost all) the violence between the IRA and Protestant terrorist groups is 20 years old. But it has been a tense peace, and thousands of illegal guns remain in Ulster homes.

A return to violence is extremely unlikely. But the coalitions holding Stormont together are falling apart.

If Northern Ireland had a border poll, would respondents move as quickly toward Ireland as the Scots have toward independence? Certainly not, since the Republic of Ireland is a real state with real problems, as opposed to an independent Scotland that can remain, at least until polling day, a repository of unlimited aspirations.

But that doesn't change the material facts on the ground. Catholics (or Catholic-descended) Northern Irish are rapidly heading toward a majority of the population. Catholics outnumber Protestants in Belfast already, as well as in schools and universities. Meanwhile, Northern Irish Protestants are more likely to move to England and stay there as adults.

Unionists may console themselves with a set of polls in 2011 that showed more Catholics expressing a wish to stay in the union rather than join the republic. But would they remain committed if Ireland's economy rebounds and the U.K.'s deteriorates? What if the broader project of the United Kingdom decomposes in the face of Scottish nationalism? And why would pro-union Catholics vote to stay in the union, when unionism will be championed by parties that attract zero Catholic votes?

Another question may be more disquieting to loyalists: Does England even want Belfast? The same polls showed that a smaller percentage of English people are committed to keeping Northern Ireland. For many years, it has received the most public money per capita in the union, while generating the least. And many English find Northern Irish politics exasperating, its style of unionism oafish.

Even Thatcher seems to have contemplated cutting Northern Ireland off during the Hunger Strikes. Similar threats were made by Westminster in order to broker the 1998 Good Friday agreement. It's hard to imagine David Cameron or his successor giving emotional speeches about the role of Northern Ireland in the United Kingdom, as Cameron and his associates have done for Scotland.

Northern Ireland's status in the union has been scrambled for some time. At the 2012 Olympic Games, Northern Irish athletes were not automatically made part of team "Great Britain," since Northern Ireland is not part of Great Britain, only the United Kingdom. Seven of its athletes competed for Great Britain, while 13 represented the Republic of Ireland.

All of this has given loyalists cause for worry.

In recent weeks, many Orangemen traveled to Edinburgh to join pro-Union parades. Indeed, the Troubles have started to figure in the mind of Scottish unionists. Emotional appeals have been made on behalf of more than 100 Scots who died serving in Northern Ireland during those dark years.

Meanwhile, Sinn Fein's leaders have been pushing harder than ever for agreements on parades, flags, and boutique nationalist concerns like Irish-language services. They are confidently declaring, "The Orange state is gone forever."

Young Catholics occasionally riot. Loyalist frustration has occasionally spilled out into rioting in recent years. And why shouldn't they feel under fire? Ireland's Constitution guarantees rights to Northern Protestants. But nothing the Republic can do will shore up the status of loyalists. Even someone like myself, whose mother wore a Bobby Sands bracelet, can see that the republican cause in the form of a border poll threatens to turn Ulster's unionists from a bare majority in a polity that matters to them to a very small minority in a republic that was seen as a mortal enemy and source of terror to their parents and grandparents.

Very naturally, Irish loyalists treasure the union more than anyone else. They fought harder than others and suffered more for the United Kingdom. Northern loyalists feel particular affection for Scotland and believe they have a shared identity that crosses the sea. Scotland's departure would be an enormous blow.

But it's important to remember that the peace process did not achieve its happy-enough result on principle, but on mutual exhaustion and disgust at oceans of bloodshed. It was patched together with false promises about what would be guaranteed to unionists and made available to republicans. In many ways, it substituted changing the status quo on a political settlement with changing the status quo on violent political action. Scotland's referendum throws the political settlement into doubt, since it highlights unionism's declining ideological appeal and the changing demographics of the region.

A 32-county Ireland is probably inevitable, although I doubt anyone will be thrilled when it comes. And Scotland must be about its own business. But in the meantime let's hope that what has been deemed unthinkable in Northern Ireland remains that way.