Newspapers are pictured in London on Friday after the referendum. (Daniel Sorabji/Agence France-Presse via Getty Images)

Danielle Allen is a political theorist at Harvard University and a contributing columnist for The Post.

We think Brexit is a European story, but it’s not really. A stable world order is hard to come by, and the United States has done more than its fair share to generate this instability over the past two decades: Think of the Iraq War, all those junk mortgage-backed securities and the global financial crisis they generated, declining U.S. foreign policy engagement with Europe, even the invention of social media. We might not want to roll back every development, but we should understand how they all contribute to a more turbulent world. And we should take responsibility.

In Iraq in 2001, Saddam Hussein was performing a fiction of possessing weapons of mass destruction, in all probability to keep Iran at bay, thereby achieving some sort of balance of power between his minority-Sunni regime and Iran’s Shiite one. We upended that order and enflamed the region. As Charles Krauthammer wrote in The Post in 2005, the George W. Bush administration had achieved a “breaking of the ‘dictatorial stability’ ” in the region. From this, he argued democracy would flow, as people rose in the streets. Weeks after the first vote of the Iraqi people, the Lebanese ousted the Syrian-backed regime, and then the Syrian military in 2005, and that was the beginning of what came to be called “the Arab Spring,” a wave of revolutions in North Africa and the Middle East that were greeted initially with optimism but have now brought us civil war in Syria and Iraq. And a refugee crisis in Europe. Some of the most politically explosive images in news in Britain in the past few years have been photos of the hundreds of thousands of refugees struggling across the Mediterranean to reach the European Union. The rise of anti-immigrant sentiment in Europe, including in Britain, has been fueled by the Syrian crisis; the roots of the Syrian crisis can be traced back to our invasion of Iraq.

After months of campaigning, the "Leave" camp has won and Britain will be leaving the E.U. The Post's Adam Taylor talks about what that means for the country and Europe. (Adam Taylor,Jason Aldag/The Washington Post)

Then there was the global financial crisis of 2008. To be sure, bankers in London contributed their fair share to the speculation-driven upswing of leverage in the global economy. But at the end of the day, the massive increase of trade in mortgage-backed securities was driven by an overheated U.S. real estate market that took the controls off of lending. Bush wanted to push homeownership but generally steered away from regulation. Unscrupulous lenders, incautious home-buyers and greedy bankers, mostly in the United States, combined to generate conditions for a worldwide recession. One of the consequences of that recession? A turn to austerity policy in Britain, the first major push of David Cameron’s administration. He held out the prospect of Britain turning into another debt-broken Greece and began slashing budgets, restructuring welfare, immigration, education and health care to do so. The austerity effort deepened and prolonged the economic pain in Britain, compared with the experience in the United States. The threat to social benefits heightened tensions around immigration from both within and outside of the European Union. The “Leave” campaign in Britain plastered buses with advertisements reading: “We send the EU £350 million a week; let’s fund our NHS [National Health Service] instead.”

Bush-era policies are not the only causes here, of course. The Obama administration’s foreign policy has involved an important “pivot to Asia,” a “rebalancing” of U.S. attention and interests to East Asia from Europe and the Middle East. The United States hasn’t achieved stability in the Middle East, and it hasn’t been there for Europe through its recent crises — from the 2008 Great Recession through the Greek debt crisis to the Syrian refugee crisis. During the Greek debt crisis, I had the occasion to ask the president of the European Central Bank, Mario Draghi, whether the United States was making a difference to his efforts to stabilize Europe. I got raised eyebrows in response and little answer.

Then there is the impact of social media. Introducing Facebook in this context may seem like a category mistake, but it’s not. A great political and social invention, Facebook, along with other social media tools, has changed the world’s political dynamics, most importantly by making it possible for dissenting minorities within countries to cross an organizational threshold permitting them to convert mere voice into actual influence and to operate transnationally. Sometimes this is for good, but sometimes it is for ill. One of the most striking details in the story about last week’s murder of British parliamentarian Jo Cox was that her alleged killer, Thomas Mair, appears to be affiliated with the Leeds chapter of the National Alliance, a U.S.-based neo-Nazi organization. In February, when I wrote a column arguing that it was time for Republicans to join together to stop Donald Trump, I received a substantial amount of hate mail and hate tweets. When a friend did a network analysis of the sources, I was surprised to discover that one of the most aggressive tweeters appeared to be affiliated with the British National Party, using the handle BadboyBNP.

The United States needs to wake up to its responsibilities in Europe. On this issue, too, our choice in the upcoming presidential election could not be more consequential. While Hillary Clinton bears significant responsibility for the pivot to Asia and the failure to pay sufficient attention to Europe, she has the knowledge and experience to correct course and help us recover our national capacity to support stability in the world order. Trump, like France’s Marine Le Pen, is celebrating Brexit. He is doing so in Scotland, the part of Britain that voted most strongly for staying in the union. There he is having staff at his Scottish golf resort wear “Make Turnberry Great Again” caps. His foreign policy is farce.