Union workers of the U.S. Postal Service and their supporters demonstrate outside of a postal facility in Philadelphia in 2014. (Matt Rourke/Associated Press)

Over the past few weeks, both Hillary Clinton and Donald Trump claimed at their party conventions that they will make great strides in job creation for the working class. That, of course, isn’t surprising. But what is noteworthy is how infrequently we hear politicians in the United States talk about what kind of jobs they want to promote.

With Trump, we get promises to bring back manufacturing jobs lost to globalization and automation. As for Clinton, we hear vague terminology like “more good jobs with rising wages” paired with raising the minimum wage. What we don’t hear often is bringing back union jobs or employment that’s protected through collective bargaining. Apparently, the candidates believe that such specific rhetoric wouldn’t resonate with voters.

As political scientists have long noted, lackluster union presence is largely an American phenomenon: The United States consistently ranks near the bottom among developed nations in terms of union membership. According to the most recent data from the Organization for Economic Cooperation and Development, about 10 percent of U.S. workers were part of a union in 2013, meaning that only a fraction of Americans are organized to negotiate their wages or benefits with employers. In contrast, the Scandinavian countries — which are often characterized as the most free-market economies in the world — have union membership hovering somewhere close to 70 percent.

Unionized labor used to be higher in the United States — around 35 percent of jobs in 1945 — but even then it lagged far behind its European counterparts. Economists partly attribute the decades-long decline in union membership to economic trends. We lost many of the traditionally unionized jobs in the manufacturing sector — more specifically those jobs that have made up the heart of the industrial Midwest economy — in the ’70s and ’80s. Still, developed countries around the world faced the same economic pressures and their unions seemed to fare just fine.

In fact, you could say that unions have thrived elsewhere in the world, especially as they became more politically involved. The labor movement has roots in a philosophy that’s deeply critical of capitalism — going back to the pre-industrialized mid-1800s. But as free-market models began expanding globally, labor unions increasingly got tangled up in the democratic capitalist systems, becoming a vital tool in governance.

In political science terms, this is referred to as “corporatism,” where the power of labor unions is balanced equally against the power of businesses and the government. You see this prominently in the United Kingdom or social market economies like Denmark or Sweden. Simply put, it’s a political system organized to balance different interest groups against one another, placing the government as a neutral third wheel to moderate disagreements.

For many union advocates, the lack of labor powers in the United States is the reason we don’t have the expansive social welfare programs that are typical of European countries (such as paid family leave programs or tuition-free college as an investment toward human capital). European unions helped to stymie wealth inequality, such as the income gap seen in the United States.

But high unionization does come with trade-offs. Some economists argue that the United States has been better off without the inflexible labor market that the unions of Europe created. And indeed, the labor market in the United States recovered from the Great Recession much more quickly than those in Europe.

We’re going to see pundits fight about which economic system is better for a long time. But perhaps it might be more fruitful to examine how we got here in the first place. The United States has had a long and complicated relationship with unions. When you look back to the labor movement at the turn of 20th century, it’s a time filled with violent strikes and nasty conflict. Politically, it’s attached to radical populist figures such as Eugene V. Debs and Bill Haywood — and none of them ever got their socialist agendas very far.

Over the course of the past century, the public has slowly been losing confidence in labor unions. By the time we got to the ’80s, voters solidly supported Ronald Reagan as he fired the country’s striking air-traffic controllers. Today, however, Sen. Bernie Sanders (I-Vt.) and his “democratic socialists” may be bringing a more positive understanding of unions back into view.

Still, from the past to the present day, labor in the United States simply never seemed to have the same political power that it did in other countries. But why not? What does this say about our political and economic systems? Why didn’t we see corporatism take root here as it did in Europe? What factors have contributed to relatively weak unions in the United States, and can they be changed?

Over the next few days we’ll hear from:

Kimberly Phillips-Fein, history professor at New York University

Michael Wasser, senior policy analyst at Jobs With Justice

Cathie Jo Martin, political science professor at Boston University

Joseph A. McCartin, history professor at Georgetown University