A little more than a century ago, socialism might not have been a mass force in American politics, but it seemed destined to become one.

In 1912, the Socialist Party won almost a million votes in the presidential election, had a membership of 120,000, and elected more than a thousand socialists to office. Mayors of cities like Berkeley, Flint, Milwaukee, and Schenectady were all socialists. So was a congressman, Victor Berger, and dozens of state officials.

That year, Oklahoma alone was home to eleven socialist weeklies. And in clusters of the country—from the Jewish enclaves of the Lower East Side to the mining towns of the West—the “cooperative commonwealth” was the dream to which all other political appeals were compared.

That commonwealth never came into being, and the decades that followed would be less kind to the Left. There were still upsurges and victories, of course, and socialists acquitted themselves well, helping build campaigns against oppression and exploitation. But as we entered the twenty-first century, socialism in the United States felt less like a live current and more like a dying piece of American history.

With the emergence of the Bernie Sanders campaign and new movements for democracy and freedom, this may be beginning to change. The events of this year all point to the emergence of “Sanders Democrats,” a group that is disproportionately young and calling for massive redistributions of wealth and power. Sanders is only the beginning; this force will continue struggling for a different sort of politics.

Over the past six months, we’ve had more conversations about socialism with friends and strangers alike than in the last six years. Jacobin’s subscriber rolls have increased by hundreds every week, and our inbox is flooded with emails asking basic definitional questions about socialism.

We don’t have all the answers, but this book was made to help tackle some of them. The ABCs of Socialism will be useful for years to come—not only as a primer for future generations of radicals, but also as an artifact of a time when the socialist left was once again filled with promise. How this story ends is up to us.