(Matt Cardy/Getty; Vladimir Simicek; Don Emmert/AFP/Getty; Albin Lohr-Jones; Matt McClain/The Washington Post)

If you had to sum up 2016 in one word, you might choose “populism.”

Once rarely used outside the academic halls of political science departments, that word has been fully cemented in the mainstream this year as shock-voting results emerged around the world. Soon, we found ourselves debating not only populism, but also economic populism, authoritarian populism, radical populism and so on.

For such a ubiquitous word, it can be surprisingly hard to say what populism actually is. Academics have offered differing definitions for decades. The evidence suggests that a populist in one country may not necessarily look like a populist in another country. “Populism has always been a misused and misconstrued concept, and this has become worse in past years, simply because of the explosion in the use of the term,” said Cas Mudde, an academic at the University of Georgia who wrote the book on the populist radical right.

Mudde says that many use the word to simply denounce a politician who is not serious or who offers simplistic solutions to problems. In fact, while definitions do vary, the core of populism is a concerted anti-establishment posture: It's us (“the people”) vs. them (“the establishment").

A distrust of the elite and pandering to the masses has been around before 2016, of course. So how did it come to dominate our understanding of the world over the past year?

April 24: A far-right candidate's close win in Austria

An early warning sign may have come from Austria in April, when a far-right candidate, Nobert Hofer, came remarkably close during the first round of Austria's presidential election to being elected as head of a Western European state for the first time since World War II.

Hofer's Freedom Party has been around for decades. It had been founded by Nazis. But his presidential campaign played down its links to the traditional far right, suggesting that the party was “to the left of the U.S. Democrats.” Instead, although Hofer has argued otherwise, many credited the success of his campaign to his appeal as a populist. He marketed himself as an anti-establishment figure.

“Unspoilt, honest, good” was his campaign slogan. He rallied against not only the Muslim immigrants arriving in Austria but also the political elites who he said aided them.

Hofer received the most votes in the first round of voting. In a runoff round in May, he was narrowly beaten by independent candidate Alexander Van der Bellen. A subsequent rerun of the vote gave Van der Bellen a more convincing majority. Yet many were still shocked that Hofer could receive 46 percent of the vote. After Hofer's defeat, Freedom Party leader Heinz-Christian Strache suggested that he viewed the results as a victory.

May 9: 'Death squad mayor' wins Philippine presidency

Rodrigo Duterte had been mayor of Davao for two decades before he became Philippine president in June. While he came from a local political dynasty, he was the first leader of the Philippines from the southern island of Mindanao and campaigned on recognizably populist pledges to upend Manila's traditional political elite and protect the poor.

Duterte won the presidential election comfortably, garnering 6 million votes more than his closest rival. His crude, sometimes bellicose rhetoric and his denunciations of U.S. power probably helped. But it was his remarkable promise to take the bloody extrajudicial war on drug dealers he had started in Davao national that gained the most attention.

Since he has assumed the presidency, thousands of suspected criminals and gang members have been killed in murky circumstances. There has been widespread international condemnation of these slayings, but the Philippine president has laughed it off with jokes that he should leave the United Nations. In fact, he has gone further — seemingly admitting to killing people himself — but it has made no dent in his remarkable popularity.

June 25: Britain votes to leave the E.U.

Britain's infamous “Brexit” vote — the remarkably close referendum that resulted in a decision to leave the European Union — demonstrated that populist sentiments held sway even outside traditional parliamentary and presidential elections. Anti-E.U. firebrand Nigel Farage had long been unsuccessful in gaining enough votes to become a member of Parliament, but his U.K. Independence Party helped define the Brexit campaign.

With UKIP's influence, what could have been a debate over mundane and bureaucratic E.U. details was suddenly portrayed as an ideological battle between a pro-Europe elite and a Brexit-backing underclass. Even relatively mainstream right-wing politicians, such as Conservative lawmaker Michael Gove, used anti-establishment language to dismiss studies that showed the benefits of the E.U., telling journalists that “people in this country have had enough of experts.”

Combined with legitimate concerns about the E.U. — not to mention plain-old nationalism and xenophobia — it became a powerful argument. And the political elite were indeed crushed by Brexit's victory: Prime Minister David Cameron, who had pushed for Britain to remain in the bloc, announced his resignation after the vote, temporarily plunging the country into political and economic uncertainty.

“UKIP used to protest against the establishment,” Farage observed after the vote, “and now the establishment protests against UKIP.”

Nov. 8: Trump is elected U.S. president

Can a billionaire who surrounds himself with other billionaires really be a populist? That's a question to consider when reviewing the rise of Donald Trump, a businessman-cum-reality-TV-star who forged an unlikely path to the White House.

Trump is clearly a member of the elite, but his campaign resonated with American voters who felt that political elites had forgotten them. His promises to “drain the swamp” in Washington suggested a new start that would wipe the slate clean for America. When it came time to vote in November, his support was stronger than expected in the economically troubled Rust Belt, helping clinch an electoral college win, if not a popular-vote victory.

Trump is an awkward fit for populism (an “anti-establishment elitist” is one description Mudde has used), but he's happy to be associated with the global wave of populism. After dubbing himself “Mr. Brexit” on the campaign trail, he invited Farage to Trump Tower in Manhattan after the election. He has even called up the Philippines's “death squad” president and spoken warmly to him, Duterte said.

Dec. 4: A referendum's defeat in Italy

Italy's populist moment was a strange one. In it, Beppe Grillo, a self-proclaimed populist, and his Five Star Movement party didn't actually advocate change — they opposed it. And to block it, they joined forces with establishment figures such as former prime minister Mario Monti.

The setting for this battle was a big referendum on constitutional changes sought by Prime Minister Matteo Renzi as a way of simplifying his country's political system and ending political gridlock. Renzi's critics — some of whom, but not all, were populists — said it was a power grab by the ambitious prime minister. Many Italians agreed; Renzi resigned after he lost the vote.

To many, the referendum result was a sign of Grillo's growing clout. The former comedian's anti-corruption message was clearly appealing in Italy, but his ideas about leaving the euro zone (not to mention links to Russia-promoting fake news websites) cause broader concern in Europe. With new elections widely predicted, some polls have shown that the Five Star Movement may be the most popular in the country.

“Times have changed,” Grillo wrote after the election. “The sovereignty belongs to the people again — and now we will really start to apply our constitution.”

Dec. 13: Impeachment in South Korea

It's certainly tempting to view the protests that eventually led to the South Korean president's impeachment as populist: Protesters were genuinely angry about a perceived unfairness in Korean society, where elites such Park Geun-hye and the shadowy figures who advised her seemed to act with impunity.

“There is a growing clamor for real political reform, real generational change and cleaner politics,” Lee Chung-min, a professor of international relations at Yonsei University, told The Washington Post this month.

But no populist politician or movement has been able to take advantage of this distrust of elites. That may change. Lee Jae-myung, the outspoken mayor of Seongnam city, is slowly becoming a possible contender in the next national election. His meteoric rise has been linked to anger over Park's scandal, and some have labeled him “Korea's Trump.”

“We have been ruled by a small class of the privileged,” Lee said at one rally in which he called for Park's removal. “Let’s make with our own hands a democratic republic where everybody is treated equally.”

What's next?

Even after this bumper year, there is plenty of room for populism to spread. Next year, there are major elections in France, Germany and Holland, where it is probable that populist-leaning parties or candidates will do well, although they are unlikely to form governments. The political crises in Britain, Italy and South Korea will no doubt continue.

Is the tide of populism reversible? Some academic research has shown populist parties notching successes in rich democracies over the past few decades. But Mudde cautions that the gains are not quite as dramatic as some would fear.

“In the 12 European parliamentary elections of 2016, far-right parties (most are populist) gained on average just 4.2 percent of the national vote!” he says. “Moreover, in Latin America, populism is on the decrease, after a successful run in the late 1990s and early 2000s.”

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