Sentiments were similar back in the 1920s, the last period of high levels of corporate concentration and inequality. Isolated protests against big business erupted periodically then as they do now. People who lived in small towns fought the grocery giant A&P’s displacement of local retailers; farmers rallied against the control Wall Street banks had over the agricultural industry; and residents of big cities protested the high prices charged by holding companies that had gained control of the electricity supply.

It was Franklin Roosevelt who helped define these scattered struggles as being about the same root problem: monopoly. At the Democratic Party’s national convention in 1936, Roosevelt devoted much of his speech to the problem of “industrial dictatorship.” A small group of powerful corporations and banks, Roosevelt declared, “had concentrated into their own hands an almost complete control,” such that many Americans were “no longer free” and throughout the nation, “opportunity was limited by monopoly.”

With voters’ support, Roosevelt set about taking up the country’s dormant antitrust laws and empowering those charged with their enforcement in the Justice Department’s antitrust division. He hired Thurman Arnold, a former small-town mayor and feisty lawyer from Wyoming, to run the division. Arnold believed that, in order to take on behemoths like DuPont and AT&T, he had to connect the division’s work directly with people’s lives. Soon after assuming his post in 1938, he published his thoughts on the matter in The New York Times Magazine. Titled “An Inquiry into the Monopoly Issue,” the piece made the case that the concentrated control of industry “is a tax on the public and a threat to democracy.” It was illustrated with a drawing of a larger-than-life cop keeping the road to opportunity clear for a stream of workers, farmers, and small businesspeople.

Under Arnold’s direction, the antitrust division opened field offices across the country to detect and investigate violations. By 1940, its caseload had grown eight-fold. With each case it prosecuted, the division began issuing extensive statements explaining to citizens what was at stake and why it was acting.

Anti-monopoly policies remained a cornerstone of American politics for decades to come, under both Democrats and Republicans. Harry Truman returned repeatedly to the issue in his State of the Union addresses. In 1950, he urged a redoubling of efforts to curb monopoly, lest the economy “fall under the control of a few dominant economic groups whose powers will be so great that they will be a challenge to democratic institutions.” Later that year, he signed legislation giving federal regulators more leeway to block mergers.

Dwight Eisenhower also embraced the importance of “checking monopoly,” as he put it in his 1956 State of the Union. Eisenhower had grown up in a Kansas farming community, where, for a time, his father owned a general store. As president, he created the Small Business Administration to “make certain that small business has a fair opportunity to compete.” In his last State of the Union address, delivered in 1961, he attributed the strength of the U.S. economy to his administration’s “vigorous enforcement of antitrust laws over the last eight years and a continuing effort to ... enhance our economic liberties.”