What's at stake in the French election

— -- Some 47 million French voters are set to head to the polls on Sunday in what could be one of the most consequential elections France has held in decades.

On the ballot are 11 candidates who span the political spectrum; if no single candidate garners a majority of the votes, two will advance to a run-off vote to be held in two weeks.

The week leading up to the vote saw President Donald Trump and former President Barack Obama wading into the campaign half a world away, as well as a terrorist attack in Paris put the country on alert.

The vote could pose an existential threat for the European Union -– a major U.S. ally that has sustained a battering by last summer's Brexit vote -- the decision by the United Kingdom to pull out of the EU.

But what's all the fuss about? And why should we care?

Here's what you need to know.

Populists at the polls

"In this year's French election, voters face an almost existential question: what type of country should modern France be? A liberal and tolerant nation conducting economic reforms at home and playing an active role within the EU and in international affairs? Or a more closed nation, unwilling to undertake structural reforms, pursuing an anti-globalization and anti-EU agenda?" said Erik Brattberg, director of the Carnegie Endowment for International Peace's Europe Program.

Many of the same forces that elevated Donald Trump to the U.S. presidency and saw Brits vote to Brexit are at play in France.

Ethnic and religious tensions have been stoked by repeated terror attacks. Unemployment has been stuck at around 10 percent for nearly five years. France's economic growth was meek in 2016 -– estimates put it just above 1 percent.

These factors are driving frustration and anger in large parts of the country. The question is how will that translate on polling day.

"With populism and anti-establishment anger surging on both sides of the Atlantic -– leading to Brexit as well as Trump's election –- the French election will provide a critical indicator of whether the populist wave is still building, or beginning to subside," Charles Kupchan, senior fellow at the Council on Foreign Relations, told ABC News in an email.

The candidate who is seemingly poised to gain the most from the discontent is Front National leader Marine Le Pen.

Seen as a political ally of Trump and the United Kingdom's so-called Brexiteers (both of whom she has praised), Le Pen is among the frontrunners going into Sunday's poll.

Le Pen and Trump "both want to be tough on immigration and both have been accused of racism," Philip Crowther, a correspondent for France 24, explained to ABC News in an email.

Her candidacy is somewhat tarnished, however, by her father’s reputation. The elder Le Pen led the Front National party before his daughter, and was widely rebuked for calling Nazi concentration camps "a detail of history." Marine Le Pen has denounced these remarks.

She has taken a strong stance against illegal immigration and championed anti-globalist sentiments.

On immigration, she has said that those who enter France illegally "have no reason to stay in France, these people broke the law the minute they set foot on French soil."

And that strong stance could pay dividends.

"Confronted with a wave of immigrants in recent years, coupled with a succession of terrorist attacks, France and other European societies are experiencing heated debates about immigration and the integration of minorities into society," Kupchan said.

Le Pen –- along with some other less popular candidates -– has also proposed a referendum on France's membership in the E.U. Many have dubbed the hypothetical vote "Frexit."

The fresh-faced Frenchman

But her victory is far from guaranteed.

Leading recent polls, but just barely edging Le Pen, is 39-year-old Emmanuel Macron -– a political newcomer who has never held elected office.

A centrist who wants to see France remain in the E.U., the political neophyte "is seen as the candidate most likely to stop Le Pen in her tracks," Crowther said.

Previously appointed as economy minister by the current (and widely unpopular) government, Macron quit his job in 2016 and formed the En Marche! party, which now claims a quarter of a million supporters.

His political platform earned him the tacit support of none other than President Obama this week, who called Macron to wish him well. Obama's spokesman was quick to note that this was not a formal endorsement; however, the two are seen as political allies.

Macron and Le Pen face strong competition from conservative Francois Fillon and far-left candidate Jean-Luc Melenchon.

Continental quandary

While Sunday's vote will almost certainly not determine the presidency –- every election since 1965 has gone to a run-off -– it will determine which two candidates will contest the final vote on May 7.

Analysts say that this French election could prove to be a matter of life and death for the European Union –- the bloc of democratic European countries that grew out of a desire for cooperation after the strife of World War II.

"Depending on who is elected, the European Union, the United States' major trading partner, is in danger of crumbling," Crowther said.

The U.S. and E.U. are strong diplomatic allies on the international stage, and commerce between the two represents the largest bilateral trade relationship in the world.

Within the E.U., France is the third largest economy (after Germany and the soon-to-be-exiting United Kingdom).

A French decision to leave the E.U., "would undermine Europe even more than Brexit, at a very crucial time," Carnegie's Brattberg said.

Kupchan agreed, saying: "If Le Pen or Melenchon were to win and seek to guide France out of the E.U., the European project might well collapse. Britain is already in the process of quitting the union, which would likely not survive a French departure.

"A collective Europe remains America's best partner in the world," he continued. "To see the E.U. unravel and Europe's separate nation-states and borders come back to life would constitute a historic setback. Especially in the face of rising challenges from non-democratic states like Russia and China."

Yet, Le Pen's promise to put France first appears to have strong appeal among a support base that is wary of Europe's largely open borders and the broader forces of globalization.

Similar sentiments have propelled two shock votes elsewhere in less than a year. Sunday will see whether Le Pen can capitalize on them within her country –- and thus put herself on a path to shake up the whole of Europe.