A specter is haunting the 2016 Democratic Party primary. The specter of socialism. Bernie Sanders's presidential bid is forcing Americans to reckon with an ideology that has profoundly shaped the politics of just about every other developed country, and has shaped America more than we might like to admit.

According to Sanders, socialism — or "democratic socialism," his preferred formulation — is basically mainstream Democratic Party liberalism but more so. It entails single-payer health care, not Obamacare. It entails tuition-free college, not subsidized loans. It entails government jobs to deal with our unemployment problem, not stimulus through tax breaks. These are big policy changes, but they also don't really seem to amount to the overthrow of capitalism — especially since actually existing capitalism in the United States has long included regulation of business and a welfare state.

But Sanders isn't wrong. Looking at the history of socialism as a movement — from its utopian beginnings to Marx's refinement and popularization and the split of socialists into reformers and revolutionaries at the start of the 20th century — reveals an ideology that has changed over time and shaped most countries around the world, including the United States, and that in some ways just isn't as sharp a break with a status quo as the pearl-clutching tone of Anderson Cooper's questions might lead you to believe.

1) Is Bernie Sanders a socialist?

Sanders is, in his own words, a "democratic socialist." To him, that means he supports the policies in place in many democratic countries, particularly Northern European ones like Sweden, Finland, or Denmark.

"In virtually all of those countries, health care is a right of all people, and their systems are far more cost-effective than ours, college education is virtually free in all of those countries, people retire with better benefits, wages that people receive are often higher, distribution of wealth and income is much fairer, their public education systems are generally stronger than ours," Sanders told Vox's Ezra Klein earlier this year. "When I talk about being a democratic socialist, those are the countries that I am looking at, and those are the ideas that I think we can learn a lot from."

That set of policies — often called "Scandinavian social democracy" or the "Nordic model" — was adopted largely at the instigation of Sweden, Norway, Finland, and Denmark's "social democratic" parties, which serve as their countries' primary left-of-center political entities, usually in conjunction with agrarian parties as a "red-green" coalition.

Over the course of the 20th century, as those parties took power across the region, they gradually cobbled together a large, comprehensive safety net, where programs were generally universal — think free health care for all, not Medicaid-style free health care just for the poorest — and which, because of that, came to enjoy wide public support. The agrarian parties are largely to thank for the universalistic aspect; farmer income tended to vary considerably, which made non-means-tested benefits attractive. Enabling and sustaining this system were large and powerful labor unions. In Sweden, Finland, and Denmark, a little under 70 percent of workers are in unions, which also run the countries' unemployment systems; many non-union members are nonetheless covered by collective bargaining contracts.

To Americans, this may just look like a hardcore version of the Democratic Party platform. But social democratic parties have traditionally identified as socialist, and emerged out of socialist movements. And historically, social democracy developed not as a more moderate form of capitalism, but as a revised and refined version of Marxism.

2) Okay, so what's social democracy, and is it different from socialism?

Social democracy is a version of socialism that emphasizes the need to achieve socialist goals — worker empowerment, a more even distribution of wealth and income, universal access to health care, education, and other essential services — through representative democracy rather than through revolution. It's the version of socialism that's enjoyed the most real-world success, both in the Nordic countries and in other rich nations, and it's the version that the main left-of-center parties in all European countries, many Latin American ones, and Australia and New Zealand embrace.

The term "social democrat" dates back at least to 1848, when Karl Marx used it to translate the name of a left-wing party of the French middle class that he disliked. By 1875, it was being used in the name of the Social Democratic Party (also known by its German acronym, SPD), which has been the dominant German socialist party ever since. But it only became a clearly distinct approach to socialism in the late 1800s and early 1900s, when, a few decades after Marx's death, a historically consequential debate broke out between two prominent members of SPD: Eduard Bernstein and Rosa Luxemburg.

The basic question was whether socialists should work toward revolution and the outright collapse of the capitalist system — or whether they should work to pass social reforms that make capitalism more humane.

Bernstein favored the reformist approach. Socialists, he believed, should abandon the goal of bringing capitalism to a point of crisis and achieving some final socialist end state. The point of having a socialist movement is not to "achieve socialism" in some sense, but to exist as a force pushing to make life better for workers. "The movement means everything for me," Bernstein famously wrote, "and … what is usually called 'the final aim of socialism' is nothing."

Luxemburg thought this was rank apostasy. It contradicted the Marxist theory that capitalism was prone to crisis and would, in time, develop to a point at which it would collapse and give rise to socialism. Bernstein's version of Marxism suggested that such a revolution may not be necessary — and indeed, that socialist goals were best achieved not through revolutionary foment but merely by passing social reforms.

"According to scientific socialism, the historic necessity of the socialist revolution manifests itself above all in the growing anarchy of capitalism, which drives the system into an impasse," Luxemburg wrote. "But if one admits with Bernstein that capitalist development does not move in the direction of its own ruin, then socialism ceases to be objectively necessary."

This debate, between reform and revolution, predated Bernstein and Luxemburg, and it continued after them. But their dispute clarified it as the central divide among socialists in the early 20th century. Luxemburg was critical of Lenin and the Bolsheviks in Russia and wary of the failed communist revolution in Germany in which she participated (and perished). But she helped lay the theoretical groundwork for that general approach, of achieving socialism through revolt and mass social upheaval. Bernstein, in turn, established a socialist tradition in which electoral politics was of the utmost importance. This became the strategic inspiration for the SPD, the Socialist Party in France, and just about every other Western European country's major left party.

In this, Bernstein was helped by the existence of non-Marxist "ethical socialists," who, unburdened by Marx's focus on capitalism's tendency toward crisis, also tended to emphasize social reforms and electoral politics ahead of revolution. The most important group here was the Fabian Society in Britain, which grew to be a key intellectual hub of the nascent Labour Party.

3) What's the difference between socialism and communism?

This one is complicated. On the one hand, "socialism" and "communism" are technical terms in Marxist theory. On the other, they're disparate political movements that have developed on the international left for a century (not to mention that socialism predates Marx by quite a bit).

In Marxist theory, socialism and communism are both as-yet-unrealized stages of humanity's economic development, with the former preceding the latter. Socialism succeeds capitalism, and is heralded by the working class's seizing of the state. Using that power, the working class then assumes control over the means of production, either by establishing cooperative enterprises in which companies are owned by their workers, or by effecting state ownership. Workers are compensated in relation to their contribution to society.

Communism, by contrast, is achieved as the state gradually "withers away," and the extreme technological progress enabled by socialism leads to such abundance that ownership and private property become essentially irrelevant. Classes evaporate, and all human needs are met.

But it's worth distinguishing communism and socialism as political movements aside from the terms' theoretical connotations. With the success of the Bolshevik revolution in 1917, socialist and social democratic parties across the world faced a choice. They could support Lenin and his allies as fellow socialists who actually succeeded in overthrowing the capitalist state through a worker's revolution, or they could oppose them as authoritarians who were abandoning the essentially democratic spirit of socialism.

This led, in Europe and America, to a split in socialist parties into pro-Soviet communist parties and more traditional social democratic parties. For example, in the US two pro-Soviet parties (the Communist Labor Party and the Communist Party of America) split off from the Socialist Party of America, before merging to form the Communist Party USA. The French Communist Party, similarly, was formed by a breakaway faction of the French Section of the Workers' International (SFIO), the country's social democratic party. The non-communist socialist parties were members of the Socialist International (or the "Second International," as it succeeded Marx's original International Workingmen's Association), while the Soviet Union organized the communist parties into the Communist International (also known as "Comintern" or the Third International).

How closely the communist parties' platform actually mirrored the policies of the Soviet Union varied considerably. Some parties, like those in the US and Britain, remained clearly under Moscow's thumb. The German Communist Party helped form the Socialist Unity Party of East Germany, which would run the country as a Soviet-style one-party state for a half-century. But in the 1970s and '80s, the Spanish and Italian communist parties embraced "Eurocommunism," an approach that emphasized reform through parliamentary democratic processes and that distanced them from the Soviet model. The reforms they wanted parliaments to pass were more dramatic than those of social democratic parties, but the difference was in degree, rather than in the parties' confidence in representative democracy. After the fall of the Soviet Union, many communist parties in Western Europe moderated and became, essentially, social democratic parties; the Democratic Party of Italy, the country's dominant left party, of which Prime Minister Matteo Renzi is a member, is (in part) a direct descendant of the Italian Communist Party, though Renzi himself is a former member of a centrist party that merged with the ex-communists.

Over time, non-Soviet-aligned revolutionary communism also came to be a major force. After the Soviet-Chinese split in 1956, parties across the globe aligned to Mao, rather than Moscow, sprouted up; the government of Albania abandoned the Soviets for China, and a number of communist guerrilla movements/terrorist groups, notably Shining Path in Peru, embraced a Maoist model. After the purging of Leon Trotsky from the Soviet party in the '20s, Trotskyist parties also cropped up, eventually forming a Fourth International, though none ever came to power.

So in practical political terms, "communism" has come to connote a belief in revolutionary political change or, at the very least, more dramatic and transformative democratic change than social democratic parties have advocated. "Socialism" has come to connote commitment to democratic processes and the taming of capitalism through reform. But communist parties would almost universally identify themselves as committed to the goals of socialism — more committed, indeed, than their squishy social democratic rivals. And for their part, many democratic socialists — like US presidential candidate Norman Thomas and British Prime Minister Clement Attlee — were vehemently anti-communist.

4) This is a lot of weird factionalist history. Can I get a music break?

I mean, if you don't love weird factionalist history, socialism might not be for you. But thankfully, there are plenty of great socialist tunes. Obviously we have to start with "The Internationale," a song beloved of socialists, communists, and leftists of all stripes at least since the Second International adopted it as its official anthem (the Communist Party of the Soviet Union would do so as well). Here it is sung by Billy Bragg, the outspoken British socialist and folk-rock singer:

Bragg also does a damn fine version of "The Red Flag," which is the semi-official anthem of the Labour Party, and of British socialists generally:

But it's not all anthems. The '80s synth-pop band Scritti Politti was Marxist in origin, taking its name from a misspelled version of the name of a book by Italian Marxist theorist Antonio Gramsci. While the band got less political over time, they were nonetheless the only band named after a Gramsci work to have a top 20 US pop hit, which has got to be worth something:

But my favorite Marxist band has got to be Gang of Four, named after the purged group of radical Chinese communists. Here's "Natural's Not In It":

5) Didn't the Soviet Union show that socialism can't work?

The good news is that neither Sanders nor European social democratic parties favor the creation of a Soviet-style economy or a Soviet-style political system. There are plenty of other models of socialist society, some of which have worked in practice, and many of which have never been tried.

In particular, the Nordic social democracies that Sanders praises are demonstrably economic success stories. One could fairly argue that these societies have successfully ended, or at least drastically curtailed, the worst excesses of capitalism. In 2012, the relative poverty rate — the share of the population living on less than half the median income — was only 9 percent in Sweden and 5.4 percent in Denmark. In the US, by contrast, it was 17.9 percent. Infant mortality in Finland is roughly half that in the US, largely because poor Finns get better health care than poor Americans.

Disposable income for the poorest residents — those at the 5th, 10th, or 20th percentile — in Denmark, Norway, Finland, and Sweden is higher than for their US counterparts. And while some of these countries, notably Denmark, have unfortunately restrictive immigration policies, others, like Sweden, have managed to maintain generous welfare states while being relatively welcoming of refugees. These countries aren't without their problems — high unemployment and the recent intense backlash against immigrants being prime among them — but they, in many ways, provide a better life for their most vulnerable residents than the US does.

And apart from the Scandinavians, most rich countries — Germany, France, Australia — have active socialist parties that have controlled their governments for periods. Your mileage may vary as to whether those tenures were successful, but that's a rather different question than whether Soviet socialism worked.

Maybe European social democracy is too mild to count as socialism, though, and we're only interested in models where the government or workers own and control the means of production. There are plenty of non-Soviet models for doing this. Communist Yugoslavia, for example, operated not through Soviet-style central planning but through decentralized workers' councils. That obviously didn't work out great — it was still a relatively brutal dictatorship — but other versions of workers' control have had success at smaller scales. Worker cooperatives, for example, are a surprisingly common form of corporate organization — the companies behind Gore-Tex, Norton publishers, and the Publix and Price Chopper grocery store chains are all owned by their employees. Total worker ownership hasn't been tried in a democratic society yet, so it can't be said that it doesn't work.

Democratic government/collective ownership of all companies also hasn't been tried, but there are plenty of models for how it could work. Sweden came close to attempting a version in the 1970s with the "Meidner plan," under which its trade unions would gradually buy up majority shares of every company until Sweden's workers could exercise total control over the country's corporations. That never wound up being implemented, but it represented a version of worker ownership of the means of production that doesn't entail Soviet-style central planning. Another possible approach is what Yale economist John Roemer calls "coupon socialism," in which every American would be given an equal, nontransferable ownership stake in its companies. That way, a majority of Americans could exercise direct democratic control over corporations.

6) So why does Sanders identify as a socialist?

Well, for one thing, Bernie Sanders has identified as a socialist for decades, including in the 1970s, when he held somewhat more radical views. But there is a sense in which his continued self-identification as a democratic socialist — rather than a social democrat, or even a New Deal liberal — cuts against historical trends. In Europe, the "social democrat" label has become more common than "democratic socialist" in recent decades, one indication among many of the rightward shift of developed countries' left parties from the 1980s onward.

And in the US, where "socialist" has never been a mainstream label, it's stranger still, given how much of Sanders's platform is shared by American politicians who don't identify as socialists. He supports single-payer health care, but so do 53 House Democrats. He supports full employment through government jobs, but so does Congressman John Conyers, who, while friendly with some democratic socialist groups, has not to my knowledge adopted the label himself. Overall it's hard to see the big distinction between Sanders and especially liberal Democrats like Sen. Sherrod Brown (D-OH) or the Congressional Progressive Caucus's leaders Reps. Keith Ellison (D-MN) and Raúl Grijalva (D-AZ), both of whom have endorsed Sanders.

So why take on the "socialist" label, knowing it might be an impediment? In his interview with Vox, Sanders suggested that he might not identify as a socialist if Democrats had stayed true to the labor liberalism of the New Deal, but that given the current economic policies of the party, setting himself apart is necessary. "There was a time — I think under Roosevelt, maybe even under Truman — where it was perceived that working people were part of the Democratic Party," Sanders said. "I think for a variety of reasons, a lot having to do with money and politics, that is no longer the case." If identifying as a Democrat is no longer enough to mark oneself as a politician of and for the working classes, then another moniker is needed — and "democratic socialist" is as good as any.

Further, it's worth questioning how distinct democratic socialism and New Deal liberalism really are, as a historical matter. For historically complicated reasons, trade unions in the US never formed a strong socialist or labor party, the way unions in European countries did. Instead, starting in the 1930s, the unions became a powerful faction inside the Democratic Party and injected many Bernstein-style policy ideas into the American brand of liberalism. Thus, while European center-left parties generally reflect a rightward movement of an ideology formerly committed to revolutionary socialism, the US Democrats are a leftward movement of classical liberalism that has, in a case of convergent evolution, arrived at similar ideas to the European social democrats. Sanders's identification as a socialist helps bridge the gap between these traditions, and emphasizes their essential commonality.