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The U.K. has voted for Brexit. Here’s what happens next.

Nigel Farage, leader of the United Kingdom Independence Party, reacts to news early Friday that Britons had voted to leave the European Union, at a party in central London. (Geoff Caddick/AFP/Getty Images)

After a bitter referendum campaign, the United Kingdom has voted for Brexit, making the decision to leave the European Union. This is the first time that the E.U. has lost a member and will have dramatic consequences for European politics. Although the United Kingdom has sometimes been an uncomfortable member of the E.U., it has played a crucial role, for example in helping to create a shared market across Europe and in pushing for the enlargement of the E.U. to include Eastern European countries after the end of the Cold War. Now, the U.K. has decided to leave.

Brexit will reshape British parliamentary politics

The first loser from Brexit is the man who decided to hold a referendum in the first place: British Prime Minister David Cameron. After winning moderate concessions from the E.U., he pressed for a “yes” vote. His failure to secure one has forced him to resign. Cameron’s Conservative Party has been badly split on E.U. questions for the last two decades, and one of his major rivals, former London mayor Boris Johnson, belatedly started to advocate Brexit, in what was widely perceived as an effort to challenge Cameron and his chosen successor. The Conservative Party is about to be plunged into a bitter leadership fight.

Live updates: Britain votes to leave the European Union

However, the Conservatives’ main political rival, the Labour Party, is unlikely to do much better. Jeremy Corbyn, the leader of Labour, was an ineffective and not especially enthusiastic campaigner for the “remain” side. Labour’s traditional strongholds in the north of England voted heavily in favor of leaving. Corbyn too has many enemies in his own party, some of whom will very likely use this to try to unseat him.

The splintering of the United Kingdom will accelerate

The U.K. consists of England, Wales, Scotland and Northern Ireland. England and Wales voted decisively in favor of leaving the European Union. Scotland, and to a lesser extent Northern Ireland, wanted to stay. This split may exacerbate existing fault lines in British politics. Scotland held a failed referendum on independence a couple of years ago; some voices in the Scottish independence movement are already pushing for a new referendum that might allow Scotland to leave the U.K. and remain part of the E.U. Northern Ireland’s Sinn Fein party has already said that it wants to renew its push to reunite Northern Ireland with the Republic of Ireland.

These tendencies, however, should not be exaggerated: Scottish nationalists may well decide that they don’t have the votes to win an election, and the Republic of Ireland is not necessarily enthusiastic at the prospect of sudden reunification and the associated upheavals.

Will Brexit break up the U.K.? Maybe not

Yet this vote will surely lead to increased fracturing. For example, many pro-British loyalists and unionists were part of the “leave” camp in Northern Ireland, even while Catholic nationalists were probably more in favor of “remain.” These differences may heighten tension. More directly, the Good Friday agreement that brought peace to Northern Ireland built on the connections of shared E.U. membership between the U.K. and Ireland. A U.K. withdrawal will likely damage the agreement.

Europe will be very different without the U.K. — and vice-versa

No one knows exactly what relationship the U.K. will have with Europe after the breakup. Britain is likely to now apply under Article 50 of the E.U.’s basic treaty to withdraw, which will lead to highly complex negotiations. The E.U. is not a simple international organization. European law is deeply entangled with the law of its member states, including the U.K. Disentangling the two from each other will be horrifically messy. One possible final outcome is for the U.K. to rejoin the European Free Trade Association, a club of states it helped set up before it was a member of the E.U., and become part of the European Economic Area. This would mean that the U.K. would still abide by many E.U. rules and have relatively free market access. However, it would have very little influence on how these rules were made. This, for example, will likely have serious consequences for the city of London. U.K. financial institutions have spent a decade fighting off financial regulations that they feared were intended to weaken the British financial sector, strengthening Frankfurt and Paris instead. Now, the U.K. may not have a seat at the negotiating table anymore.

Another very difficult question will be the U.K.’s relationship with the Republic of Ireland. The U.K. and Ireland joined the E.U. together; they are intimately linked since the republic used to be part of the U.K. Irish nationals get many voting rights in Britain, and vice versa, and there is free travel between the two countries. Now, the E.U.’s border is going to run along the division between Northern Ireland and the Irish Republic, creating a multitude of headaches.

Finally, the decision of the U.K. to leave will have devastating effects in the short run for the morale of E.U. leaders. The union has underpinned peace in Western Europe for most of the post World War II era. Yet in the last few years it has stumbled from existential crisis to existential crisis, thanks to the difficulties of the euro, controversies over migration and the slide of major member states such as Hungary and Poland away from standard liberal democracy. Now, one of its core members is leaving. Nationalists in other European countries are already taking note. It is possible — just about — that Brexit will allow the E.U. to consolidate more easily around Germany and France over the longer term, creating a more unified political entity. However, that would require a degree of political cohesion and shared vision that is not apparent right now. More plausibly, the decision of the U.K. to leave will strengthen the forces that are pulling E.U.member states away from each other.

This is not great news for the U.S.

The “special relationship” between the United States and the Britain has often been exaggerated. In recent years, Washington has turned more of its attention to Asia, and when it pays attention to Europe, discussions are more likely with Berlin than London. Nonetheless, the U.K. has played a very valuable role for the United States in Europe, pressing common interests, a broadly similar approach to free markets and a shared distrust of some common enemies.

Now that’s coming to an end. On the one hand, the United States will no longer have as much leverage within the E.U. as it had. One of its key friends is leaving. On the other, the U.K. is now likely to be less important to the United States. Bluntly speaking, it is a mid-sized regional power that has chosen to break ties with the other friendly states in its region. While it will not be a pariah, its influence — and hence its value to U.S. presidents and policymakers — will be substantially lower.