Every national election, in one way or another, is consequential. Yet Thursday’s vote in the United Kingdom has particular, and maybe even profound, importance for Great Britain, the European Union and the United States.

Like most elections in systems traditionally dominated by two parties, it’s likely that either the Conservatives, led by Prime Minister David Cameron, or Labor, led by Ed Miliband, will ultimately prevail. But polls indicate that it will be impossible to do so without forming a coalition government, like the current Conservative-Liberal Democratic alliance.

The new political partners may be different this time. Cameron might need to include the U. K. Independence Party (UKIP), whose anti-E.U. and anti-immigration sentiments have rallied some disaffected Brits. The rise of UKIP, led by Nigel Farage, is one of the reasons that Cameron has pledged a referendum by 2017 on whether the United Kingdom should remain in the E.U.

For Labor, it might mean a coalition with the Scottish National Party (SNP), whose leader, Nicola Sturgeon, has emerged as the election’s dynamic political figure. A strong SNP showing could rekindle the Scottish independence movement, and maybe even result in a new independence referendum. Last year’s referendum kept the United Kingdom just that, but the SNP’s surge creates new uncertainties for Great Britain.

With the West buffeted by multiple crises, Britain’s inward turn couldn’t come at a worse time for the E.U. or the U.S. Sure, the U.K. is still a permanent member of the United Nations Security Council, and it has been active in multilateral diplomacy regarding Russia and Iran, among other issues. But Britain’s receding leadership, at least compared with historical norms, is apparent to ally and adversary alike, and appropriately has emerged as a campaign issue.

Because Britain kept its own currency, it’s less central to the continent’s chronic eurozone crisis. But the U.K. is crucial to the E.U. unity that is badly needed to solve other problems. Most notably a revanchist Russia shows no sign of standing down regarding Ukraine, and it remains an existential threat to other European nations. Relatively robust U.S. and E.U. sanctions have had some economic, but little political, effect on Moscow, which would likely welcome a distracting debate from one of Europe’s most consequential countries on the E.U. itself.

E.U. cohesion is also needed on other fronts, especially the migration crisis sparked in part by struggling governments or outright failed states in North Africa and the Middle East.

Just like the E.U., the United States often depends on U.K. diplomatic and military support for foreign policy objectives, so it faces similar risks if a Scottish secession or E.U. withdrawal weakens Britain’s capacity or resolve. Despite crises elsewhere, President Obama and congressional Republicans should surely be able to coalesce on the need to preserve the “special relationship,” even if it is altered by Thursday’s vote.