The great grand strategists of history sometimes discounted the levers of economic power as mere means of raising armies and funding empires. With the end of the Cold War and the integration of the global economy, however, that archaic vision is receding, and a new power calculus is emerging, one with economic strength and leverage at its core. Foreign policy experts would do well to interrogate the sources of that strength. That’s the alarm Les Gelb kept sounding in his later years.

Les understood, in a way few of his high-born contemporaries could, the importance to American power of upward social mobility, economic fairness, and a thriving middle class. He knew it instinctively because he had lived it, as the child of poor but industrious immigrants from the Carpathians whose small store in New Rochelle, New York would have been their son’s future in any other country. Instead, thanks to a robust social contract and a rising postwar economic tide, Les’s natural abilities carried him far beyond his humble origins. In the last decade of his life, he was gratified to see the increasing role of economic thought in our foreign policy, a proposition he had long championed. But he also was deeply concerned that a focus on aggregate growth and the health of large corporations obscured a bleaker story playing out in the lives of everyday Americans. He repeatedly expressed his concern to us that the hollowing out of America’s middle class meant the hollowing out of American power.

Roughly 10 percent fewer American adults live in middle-class households today than did in the 1970s. Some of that attrition is owed to increasing numbers now earning upper-class incomes, but many have fallen the other way. The drop is indicative of how much has changed in the last half-century when it comes to income and inequality in the United States. When the Census Bureau began tracking wealth inequality—the standard measure of which is known as the Gini index—in 1967, the nation scored 0.397; as of last year, it had risen to 0.485. (Gini scores are like golf—lower is better.) In that same time, middle-class incomes have remained largely flat in inflation-adjusted dollars, while the combined costs of housing, education, and health care have risen astronomically. The sad result is that an increasing number of young Americans fear that they will live no better and quite possibly a good deal worse than their parents.

Such stagnation—fueled not only by the sacrifice of blue-collar jobs to outsourcing and automation, but also by grossly inadequate public education and crumbling infrastructure—is testing the resilience of America’s most important resources: the development of its diverse and creative human capital; the attractiveness of its economy and society to others around the globe; and its hopes of maintaining real constitutional democracy.

Americans deserve a foreign policy strategy that leverages the country’s collective strength on their behalf. But contrary to the populist “solutions” of the current Administration, the answer does not include destructive trade wars or bilking allies for collective defense. Instead, what’s called for is a concerted effort to connect sound domestic economic policy—including more robust government stimulus for industries producing good, sustainable jobs for American workers—with more effective international economic policy focused on fighting corruption, tax evasion, corporate concentration, and races to the bottom on labor and the environment.

Les saw this project as a pillar in a broader American strategy, one in which the United States leverages its best asset—its alliances—to shape the rules of the twenty-first century international order so that they reflect the principles and preferences of strong, fair market democracies rather than authoritarian capitalist systems seeking to accumulate and exercise power for the benefit of their elites. For Les, and for us, that strategy starts at home—with the renewal of the great American middle class.