evidence: In one sense, why should anyone outside Britain or Ireland care about a political breakdown of this nature? Northern Ireland is about the size of Connecticut, but with half of the population and nowhere near the wealth. It has no significant natural resources or strategic economic interests. In almost every way, it is irrelevant to the core interests of Europe’s great powers and certainly to the U.S., even if there are obvious moral and political reasons to resolve the dispute. [...] Both the U.K. and the EU have long known this but ignored the warnings, believing that whatever deal they thrashed out could be imposed on Northern Ireland without the consent of both sides of the political-sectarian divide there. This is essentially the position still taken by the EU, Ireland, and parts of the U.S. establishment, which have concluded that Johnson’s government—if it wished—could back down in its demands and reach a compromise with the EU broadly along the lines already agreed upon, and Northern Ireland’s unionists would, in the end, have to swallow it. [...] This analysis is clearly true insofar as Northern Ireland’s future does rely on a stable relationship between the U.K. and the EU, but it implicitly assumes that the tension is all the fault of Johnson. More fundamentally, though, the analysis also works in reverse. The relationship between the U.K. and the EU cannot be stabilized until the situation in Northern Ireland is resolved. And right now it is far from resolved. Northern Ireland today is a rot in the heart of the Western alliance that is being left untreated.