A Teamsters protest in Upper Marlboro in 2010. “Scabby” the rat is a well-known symbol used by protesters in the D.C. area. (Juana Arias For The Washington Post)

Each week, In Theory takes on a big idea in the news and explores it from a range of perspectives. This week we’re talking about unions in the U.S. Need a primer? Catch up here.

Kimberly Phillips-Fein is the author of “Invisible Hands: The Businessmen’s Crusade Against the New Deal.” She teaches American history at New York University’s Gallatin School of Individualized Study.

Why are there no labor unions in America? This is, of course, an overstatement — millions of Americans still belong to unions. But the size of the unionized workforce has declined every year for 40 years. And even at its mid-20th-century peak, it was lower than in most European countries.

Many explanations for low union density turn on the distinctiveness of American culture. Americans are deemed individualists, with self-interest trumping any sense of the common good. They are driven wild with consumer longings, willing to do anything for low prices. They are entrepreneurial, identifying with their employers and always dreaming of upward mobility or striking it rich rather than claiming solidarity via working-class identity.

One might question whether this is really an apt description of American culture. But to the degree that it is accurate, it may have grown out of our history of employer intransigence and hostility to labor.

In the late 19th and early 20th centuries, American workers literally fought battles — in Homestead, Pa.; Ludlow, Colo.; the hills of West Virginia — as they struggled to gain the right to organize unions. Until the Great Depression, employers were under no obligation legally to recognize or bargain with unions, and few did so voluntarily, instead provoking strikes that often turned bloody.

Even after Congress passed the Wagner Act in 1935, which created an institutional mechanism whereby workers could vote to join unions, major employers sought to subvert the law by spying on their workers, planning strategies to dissuade their employees from voting to unionize and, in some cases, even stockpiling weapons.

After the Supreme Court upheld the Wagner Act in 1937, companies worked together through such organizations as the National Association of Manufacturers to disseminate strategies for fighting unions. Employers staged elaborate propaganda campaigns intended to persuade workers to vote against unionization, sometimes even firing workers deemed to be pro-union in direct violation of the law.

Such tactics were one reason union density remained low outside of the core manufacturing industries that had been organized during the 1930s. It also remained low in the South and Southwest. In the South, segregationists and businessmen worked together to resist unions. In the Southwest, civic boosters sold their cities as alternatives to the high-wage Northeast and Midwest.

Over time, manufacturers closed their plants in such union strongholds as Detroit and Philadelphia, Camden and Trenton, relocating first to the American South and then eventually beyond U.S. borders — to Mexico, the Caribbean and farther overseas. The most successful companies in the burgeoning service sector — companies such as Walmart — built a fierce resistance against unionization into their business models from the start. At the same time, conservative politicians from the 1970s onward portrayed unions as inherently coercive, while liberals grew wary of passing legislation that could shift the playing field and make it easier for workers to unionize.

History has shaped the landscape for any workers who might want to organize unions today. Because of the intensity of employer opposition, workers who seek to unionize risk polarizing their communities. They may be blamed for taking actions that could lead to their towns losing the company altogether; they may even be fired themselves in retaliation. Is it any wonder that many conclude unionization is not worth the effort? Is it surprising that, despite unionized workers earning higher wages than nonunion workers and enjoying a measure of protection on the job, many consider it easier to find some way to make do and get by rather than take a leap of faith and organize?

When employers have been able to wield such political power, and when there are so many examples of collective defeat, it can seem as though acting alone is the only real way to improve your life. Over time, this comes to appear as a culture of individualism. But it might be more precisely described as a culture of fear.

Other perspectives:

Michael Wasser: Unions could make a comeback — if we help them

Cathie Jo Martin: Business and labor don’t have to be enemies

Joseph A. McCartin: This election could decide the fate of American labor — and that’s the problem