Where did Democratic presidential candidate Bernie Sanders get his political philosophy? Here's everything you need to know:

What is socialism?
Broadly, it's a political and economic system under which the means of production are owned by the community as a whole, with government ensuring the equitable distribution of wealth. But socialism has taken many forms. "'Socialism' is an exceedingly fuzzy term used to label an extraordinarily wide array of political and economic beliefs," says scholar Paul Brians. Socialism has morphed into Soviet-style communism and spawned Latin American dictatorships, while in Europe, many countries combine socialistic principles with capitalism and democracy. In the U.S., programs that opponents once condemned as socialism, such as Social Security and Medicare, are now deeply embedded in our society. Still, socialism has largely dwelled on the margins of American politics, until it was revived by the campaign of Democratic presidential contender Bernie Sanders.

What is Sanders' preferred form of socialism?
A self-described "democratic socialist," Sanders believes government should aggressively use taxes and social programs to limit income inequality and provide health care, day care, and a college education to all without charge. But he doesn't spurn private enterprise. "I don't believe government should own the means of production," the Vermont senator says. "I do believe the middle class and the working families who produce the wealth deserve a fair deal." Sanders' model social democracy is Denmark, which tops polls of the world's happiest countries — but also has one of the world's highest tax rates, averaging about 60 percent.

When did socialism arise?
It began as a response to the dire poverty and inhumane working conditions in industrialized Europe in the early 19th century. One of the first thinkers called a "socialist" was Robert Owen, an idealistic Welsh mill owner who in the 1820s created a number of short-lived "utopian" communities — basically, collectives — in Britain and the American Midwest. But socialism really took off in midcentury, spurred by the writings of German philosopher Karl Marx and the rise of labor unions. "Socialists rejected the argument that the wealthy deserve their wealth because they created it," Brians says, "instead believing that wealth is created by the working class and wrongfully appropriated by the rich."

How did it spread to the U.S.?
Mainly via Marxist German immigrants, who spearheaded the establishment of the Socialist Labor Party (SLP) in 1876. The first socialist to hold public office in the U.S. was Fred Haack, a shoe-store owner elected to the Sheboygan, Wisconsin, city council in 1897. Four years later, ex-SLP members and others formed the Socialist Party of America, which over the next two decades elected two U.S. congressmen, dozens of state legislators, and more than 100 mayors. "They pushed for public ownership of utilities and transportation facilities," says political scientist Peter Dreier, as well as expanded parks, libraries, and playgrounds "and a living wage for workers." The face of the party was Eugene V. Debs (see below), a fiery railroad-union leader who ran for president five times. But by the 1920s, U.S. socialism had fallen far out of favor.

What happened?
The Socialist Party opposed America's entry into World War I, and was widely condemned as unpatriotic. In 1917, Congress passed the Espionage Act, making it a crime to speak out against the war or oppose the draft. Thousands of socialists, including Debs, were subsequently arrested. At the same time, Russia's Bolshevik Revolution caused a "red scare" in the U.S. — a panicky fear that a similar worker revolt might occur here. Suspected radicals were rounded up and jailed, and nativists demanded an end to immigration from Italy and Eastern Europe, which they saw as hotbeds of communist sentiment.

Is socialism the same as communism?
No. Marx envisioned communism as a higher and purer form of socialism, in which all private property would become obsolete, class distinctions would dissolve, and goods and services would flow freely, "from each according to his ability, to each according to his needs." In the Soviet Union, China, Cuba, and other communist countries, Marx's idealistic vision produced a grim reality, with economic growth stalling and an authoritarian ruling class appropriating much of the meager wealth for itself while murderously suppressing all dissent. During the Cold War, "socialist" and "communist" were often used interchangeably in the U.S., in what political scientist Lawrence Quill calls "shorthand for all things un-American."

Is socialism un-American?
Many Americans have conflicted attitudes about socialism, best illustrated by the Tea Party activists who demanded that "government get its hands off my Medicare." But when a Gallup poll asked Americans last year whether they would consider voting for 11 categories of presidential candidate, "socialist" ranked last, garnering 47 percent, behind "Muslim" and "atheist." Among 18- to 29-year-olds, however, 69 percent had no problem voting for a socialist. Why the huge disparity? People in their 20s have no memory of the Soviet Union or the Cold War, but did come of age during and after the 2008 financial crisis. To young people feeling great economic insecurity, sharing the wealth sounds less like a threat than like a promise.

Sanders' socialist hero
Eugene V. Debs received 919,799 votes in the 1920 presidential election — while serving a 10-year sentence for his passionate opposition to America's entry into World War I. "The working class, who freely shed their blood and furnish the corpses, have never yet had a voice in either declaring war or making peace," Debs had said. A rousing speaker, he made four other White House bids, garnering 6 percent of the vote in 1912. Debs embraced the Russian Revolution, but was appalled by the Soviets' violent suppression of dissent; pardoned by President Warren G. Harding in 1921, he remained a vociferous anti-communist until his death in 1926. Many of Debs' ideas — such as banning child labor, social security for retired workers, and unemployment insurance — were later co-opted by the major parties. He was the subject of an admiring 1979 documentary — Eugene Debs: Trade Unionist, Socialist, Revolutionary — produced and narrated by his political descendant, Bernie Sanders.