The United States is a flawed democracy. This is not a subjective statement, but rather a rating assigned to the United States by the Economist’s annual Democracy Index. The downgrade from “full democracy” was the culmination of a decade of declining ratings, moving the United States out of a category that includes Australia, Canada and the United Kingdom and into a peer group with India, Botswana and Chile.

For decades following the successes of the civil rights movement and the passage of the 1965 Voting Rights Act, the United States had the basic ingredients that most analysts consider necessary for a functional democracy. Yet organizations that track levels of democracy around the world find that these ingredients are dwindling in the United States.

To understand why American democracy is declining, it is tempting to focus on recent events, such as the 2008 recession or state-level initiatives that restrict voting. But doing so risks mistaking symptoms of the problem for its causes. To drill down into the real causes of American decline, we should consider the conditions that have historically contributed to the collapse of democracies.

In fact, our current moment shares striking similarities with pre-World War II Europe, when the number of democracies was also shrinking rather than rising. In 1959, Seymour Martin Lipset, one of the 20th century’s most prominent theorists of democracy, identified two broad factors as critical to explaining the differences between stable and unstable democracies during this period: economic development and political legitimacy.

In doing so, Lipset implicitly challenged some of the basic assumptions the Founding Fathers had made when creating the U.S. government. In the Federalist Paper 10, James Madison identified mob rule and the rise of political factions as the main causes of democratic failure, and so the framers of the U.S. Constitution attempted to limit the power of factions by building checks and balances into their political system. But Lipset believed these measures were insufficient for preventing factionalization and mob rule. He argued that strong factions will prevail in the presence of extreme economic inequality, regardless of how the political system itself is designed.

This is what had happened in many European countries during the 1920s and 1930s. Using indicators of economic development such as per capita income, number of doctors, number of telephones and radios and percentage of men in agriculture, Lipset showed in his analysis that there were stark differences in the overall levels of development between countries that had experienced an uninterrupted continuation of political democracy since World War I vs. those that had not. For example, the average per capita income across European countries that had maintained stable democracies was more than twice that of the countries that had experienced instability.

While Lipset’s focus on the overall wealth and development of nations would not capture inequality today, at the time of his writing, more-developed countries were experiencing their highest degree of economic equality in history. His findings, thus, lent credence to his assertion that “a society divided between a large impoverished mass and a small favored elite would result either in oligarchy … or in tyranny.”

Today, Lipset’s assessment still resonates. Despite decades of growing wealth, the United States has experienced rapid increases in economic and educational inequality. Wages in the United States have risen since 2000, but five times as fast for the highest earners than for the lowest earners. With fewer union protections and less government assistance, many Americans are struggling just to get by, even as the number of millionaires in the country hit record highs. A 2017 report by the U.S. Federal Reserve Board found that approximately 40 percent of Americans reported being unable to cover an unexpected $400 expense.

Lipset contended that education was also a key safeguard against factionalization and mob rule. That was one of the reasons economic development bolstered democracies: More-developed countries were better able to provide education. Here, too, though, the United States is falling short, with declining quality of education and growing inequality in educational attainment. As the education scholar Sean Reardon succinctly summarized in 2011: “The achievement gap between children from high- and low-income families is roughly 30 to 40 percent larger among children born in 2001 than among those born twenty-five years earlier.”

Moreover, researchers have documented the increasing commodification of opportunities, showing that educational opportunities are increasingly dependent on the affluence and private resources of individual families.

When it comes to economic development, then, the United States is increasingly accruing the conditions that destabilized democracies around the world before World War II.

Nor is the United States doing well on Lipset’s other marker of democratic health: the legitimacy of the political system. He identified specific conditions that would consistently undermine the legitimacy of democracy. First among these was the way that a society deals with major political conflicts. Lipset argued that a failure to resolve important political differences as they arose increased political polarization, because those differences would become embedded in conflicts between factions.

Indeed, much of the polarization and frustration in America can be linked to the failure to resolve fundamental cleavages. Debates over abortion rights, gun rights, access to health care, voting rights and other important social issues have amassed over the past half-century along increasingly partisan lines.

Political factionalization is not solely driven by failures to find solutions to thorny issues. Lipset argued that divisive politics thrived on social and intellectual isolation, which political leaders can manipulate to build support. Such leaders need to prevent their followers from being exposed to ideas and narratives that do not fit their political argument. Indeed, propaganda and claims of “fake news” were rampant in the European countries that experienced democratic decline in the interwar years.

In the U.S. context, we have seen such threats to legitimacy grow more prevalent during the past several decades. According to the Reuters Institute’s 2017 analysis of people’s news consumption habits across 37 countries, American news consumption is among the most polarized in the Western world. Viewed through the lens of Lipset’s work, the intensification of ideological cleavages surrounding long-unresolved political issues, coupled with growing divisions over what kinds of news people consume and trust, have intensified the legitimacy crisis in the United States.

When it comes to the health of American democracy, Lipset’s study paints a bleak picture. But it offers a reason for hope, as well. By directing our attention to the same social conditions that affected the stability of 20th century European democracies, his work highlights that voting citizens — not political institutions — are the key to stabilizing and rebuilding democracy. Our institutions may be weakening, but if our people are committed to a functioning democratic system, there is still reason to hope.