Scottish National Party (SNP) leader Nicola Sturgeon confirmed on Tuesday that she will, before the end of this year, ask the UK government to approve another independence referendum. With Brexit the immediate trigger for the decision, it is increasingly possible that the 2020s could — tragically — witness the unraveling of one of the world’s longest and most successful political unions. What Sturgeon’s plans underline is that political worries about Brexit, even though Prime Minister Boris Johnson confirmed on Thursday that he has negotiated a new withdrawal deal with EU, go well beyond Westminster to the Scottish, Welsh and Northern Irish legislatures. Despite the 2017 Supreme Court ruling that the UK government did not have to consult the devolved administrations before triggering Article 50, this has not stopped politicians in Edinburgh, Cardiff and Belfast from being thorns in the side of the PM. The Scottish and Welsh first ministers, Sturgeon and Labour’s Mark Drakeford respectively, have both said that they cannot support Brexit without membership or full access to the single market, which appears highly unlikely to be realized. Sturgeon argued on Tuesday that the Brexit plan Johnson has now agreed with the EU, if ratified by Parliament, would be particularly disadvantageous to Scotland due to its hard exit from the EU. Meanwhile, there is also substantial opposition in Northern Ireland to the government’s stance, especially from Sinn Fein, whose leader Michelle O’Neill has said that Brexit “ignores the views of the majority of the people” in the country, who voted to remain by 56 percent to 44 percent. Former Sinn Fein leader Gerry Adams has also previously asserted that Brexit will undermine the Good Friday peace deal, while being a unique opportunity to “unite the island of Ireland.” His argument is that it makes no sense to have one part of the island (the Republic of Ireland) within the EU and the other (Northern Ireland) outside it. Given the opposition to Brexit of most key party leaders in Scotland, Wales and Northern Ireland, the exit negotiations with the EU have tested the UK’s constitutional and legal frameworks to their limits. But it is not just devolved authorities outside of England, but also English local government leaders who have voiced concerns about Brexit, not least given potential lost funding opportunities. With the planned repatriation of powers from Brussels, local leaders in England want to assume a greater role, rather than everything being centralized in Westminster. Take the example of Mayor of London Sadiq Khan, who has made clear his concerns about the implications of Brexit for the metropolis — a city that is home to 12 percent of the UK’s population but generates almost a third of the country’s tax income. As frustrated as some English local authority leaders are, it is in Scotland where the rubber may meet the road. Sturgeon is seeking to capitalize on popular discontent with Brexit in a nation where 62 percent of voters backed remain in 2016. While she has understandable concerns about Brexit, she is leading Scotland and the wider UK down a potential political black hole, which will probably weaken all parties given that their future is better together. It is widely accepted that the UK in general would be damaged by Scottish independence. For instance, a Parliamentary Committee warned that losing the Scottish tax base, especially at a time of fiscal austerity, could lead to further budgetary cuts to the armed forces. Moreover, the UK’s large overseas aid budget and extensive network of diplomatic and trade missions will also be impacted. Together with military cutbacks, this would undermine both the hard and soft power that has enabled the nation to punch above its weight for so long. Scottish independence would also erode the UK’s post-Brexit voice in international forums, from the UN to the G7, G20 and NATO. Perhaps, most prominently, it could be seized upon by some non-permanent members of the UN Security Council (UNSC) and/or other UN members to catalyze a review of the UK’s permanent member status. Reform of the UNSC is certainly overdue and Scottish independence could see this issue being decided upon in less favorable terms for the UK than may otherwise be the case. All this underscores that Scottish independence, combined with Brexit, would undercut the domestic underpinnings of the UK’s international influence. They threaten to undermine the sizeable political, military and economic force that the UK has preserved, helping bolster international security and prosperity. Moreover, Sturgeon is charting a course toward a second referendum despite the uncertainties about whether or not Scotland would benefit significantly from independence. Most obvious is the difference between tax revenues and public spending in the country, which rose to a deficit of about 9.5 percent of gross domestic product in 2015-16. It can better stomach this shortfall as part of the union. With growing political risks over the integrity of the union, the case again needs to be made as to why the future of both Scotland and the rest of the UK are better together. There would be significant uncertainties for Scotland from independence, while the costs to the UK are clear in terms of diminished international influence and the fraying of the remaining bonds between England, Northern Ireland and Wales. Andrew Hammond is an associate at LSE IDEAS at the London School of Economics