“Devolution”—transferring powers to the individual nations—was one of the big political projects of Tony Blair’s governments, an effort designed to contain any separatist urges, allowing each part of the union to maintain its unique identity within the whole.

The plan was driven by the realistic assessment that there was no reason the U.K. should endure as an entity, any more than the list of “vanished kingdoms” drawn up by Norman Davies in his history of Europe: Burgundia, Litva, Borussia, Aragon. The decision to establish devolved governments in Northern Ireland, Scotland, and Wales took place when the former Yugoslavia’s violent splintering was still fresh in voters’ minds.

Now, Brexit has again put the idea of Britishness under severe strain. The leader of the Scottish National Party (SNP), Nicola Sturgeon, is agitating for another independence referendum. The last one, in 2014, in which Scotland voted to remain part of the U.K., may have been billed as a “once-in-a-generation event,” but her party argues that leaving the European Union has profoundly changed Scotland’s circumstances, and its citizens deserve another say.

Read: Is Brexit worth Scotland’s independence?

Compared with this, Welsh nationalism feels like the dragon that has never roared. Certainly, there is anti-English sentiment washing around—Cofiwch Dryweryn—but its impact on the ballot box is limited. The nationalist party Plaid Cymru (the “Party of Wales”) holds just a tenth of the Welsh seats in the British Parliament (the SNP has more than half of Scotland’s) and has little chance of making net gains in Thursday’s election. Support for Welsh independence is at only 28 percent. When voters are given a range of options on further devolution, the most popular choice is to leave things as they are now.

It didn’t have to be this way. In the first devolved elections in 1999, Plaid Cymru received a higher share of the vote than the SNP. So what went wrong for Welsh nationalists—or, perhaps, what went right for their Scottish counterparts?

When it comes to separatist movements, James Mitchell tells me, “memory is more important than history.” Mitchell, a professor of public policy at Edinburgh University, has devoted his career to studying the conditions needed for states to break apart. National identity, unsurprisingly, is key—but that identity is often mythical as much as observable. When we spoke, Mitchell was in Italy, where the far-right League party of former Italian Interior Minister Matteo Salvini has invoked the concept of “Padania,” an alternative name for the Po Valley in the country’s north. Salvini contends that the region is subsidizing the rest of the country. Padania, in its own way, is as symbolic as the drowned village of Capel Celyn.

That idea of subsidy brings us to another factor: a sense of grievance—or, to put it more neutrally, injustice. Both Scottish and Welsh nationalists chafe against England’s dominance, but Brexit gives the SNP’s cause an extra boost. A majority of the Welsh voted to leave the European Union, whereas a majority of Scottish voters opted to remain. Sturgeon, therefore, can credibly claim that Scotland is “being taken out of the EU against our will.”

Scotland’s economic case for independence is stronger, too. Ahead of the 2014 referendum, Scottish nationalists argued that any decline in revenue after independence could be offset by a “North Sea oil fund.” The exact figures were endlessly disputed, particularly because of the fluctuating price of oil, but the debate created the meme that, far from being a poor relation, Scotland was a country whose natural resources had been exploited by a government in Westminster. Most Welsh jobs, meanwhile, lie within 30 miles of England, and Wales’s economy appears more reliant on its bigger neighbor, according to Roger Awan-Scully, the head of the politics department at Cardiff University.