EVERY once in a while, often with no prompting whatsoever from Scotland, people in some area of America start talking about secession. The most famous recent instance of secession talk involved comments made by Rick Perry, the Republican governor of Texas, in 2009. Mr Perry did not actually endorse the idea of Texas seceding, but said he understood why some Texans were considering it. Texas's ultra-conservative railroad commissioner took things further in 2013, lauding the state's progress in "becoming an independent nation", which he said was important in case the rest of America falls apart. There are also active, if tiny, secessionist movements in Vermont and in the South, both of which found the Scottish independence referendum inspirational. More broadly, the idea of secession tends to come up jokingly in conversation among politically active, like-minded Americans when they address some intractable political problem with a regional divide. Recent conservative moves to carve out new states in California, Colorado and Maryland were based on rural Republican resentment at living in states dominated by urban Democrats. Guns seem to be a particularly secession-prone issue, mostly among conservative gun-rights enthusiasts rather than liberal gun-control advocates. This is somewhat odd, as gun ownership and open-carry rights have been widely expanded in recent years, while many gun restrictions have expired or been defeated. The most significant secessionist movement on the left, that in Vermont, is motivated more by environmentalist antipathy to neoliberalism and the globalised corporate economy, as Christopher Ketcham wrote in a long profile in the American Prospect last year. Libertarians angered by powerful elites appear in both right- and left-wing secessionist groups, but the flavours tend to be different.

Some of the secessionists in these movements are charmingly idealistic do-it-yourselfers in a long American utopian tradition. Others are disturbing-sounding provincials hostile to the diversity of large societies. Some are community-minded folks who think smaller polities do better at serving their own needs. Others are ornery individualists who don't want the community butting into their affairs at all. Under normal circumstances, these interesting assortments of free-thinkers don't attract much support.

What interests me are the situations when secessionist movements suddenly do start to gain a bit of traction. Uniformly, that happens when a region is angry because the party it favours is losing national or state-wide elections. The current iteration of Vermont's independence movement got started in 2003, a year of intense liberal frustration that saw the Bush administration launch America's occupation of Iraq. Murmurs of Texan independence and the state secession movements in Colorado and Maryland followed Barack Obama's election wins in 2008 and 2012. Similarly, the enthusiasm behind Scotland's independence vote was heavily influenced, though obviously not limited to, the popularity of Labour in Scotland and the presence of a Conservative government in London.

What this suggests is that secession movements are to some extent a second-order phenomenon, and that the real driver is partisan hostility. When progressives decide they don't want to be part of America anymore, they mostly mean that they don't want to be part of a Republican America anymore. When conservatives decide they don't want to be ruled by Washington anymore, they mostly mean that they don't want to be ruled by a Democratic Washington. And there are two reasons why that can be the case. One is that America has very significant, authentic regional divisions: the deep South is profoundly different from the North-east, as is the conservative inland West from the liberal Pacific coast. But the other is that America's two political parties have been increasingly successful at organising different preferences into coherent ideological camps, and at carving up territory according to those preferences. With the territory carved up, liberals and conservatives increasingly move to friendly territory, sorting themselves into like-minded blocs.

In other words, the fact that different regions gradually get so angry at each other that they consider exiting their political union may not be a matter of stable regions with different innate characters being split by growing disagreements. It may be a matter of political parties transforming the political map such that regions are turned against each other. As Democrats have consolidated their dominance in Vermont, the state has turned too progressive for the national party, let alone for compromise with Republicans. As Republicans have consolidated their dominance in Texas, the state has turned too conservative for national Republicans, let alone compromise with Democrats. (Latino Democrats in Texas complicate this story, but Texas Republicans don't seem to be listening to them.) Groups of voters in both states come to feel they're not living in the right country anymore. If they call for secession, what we're seeing may not actually be a region that doesn't want to be part of America. It may be a group of extreme partisans who don't want to compromise with anyone.

In America, secessionist movements are more of a symptomatic curiosity than a real threat. The risk of a region or state seceding in America in the foreseeable future is minimal. But the risk that voters in each party come to feel they don't belong in the same country with each other is not.