One of the great challenges facing the global order over the coming decades is the aging of the population. Most high-income countries have aged continuously over the past century. Driven by a combination of low childbearing rates and improved mortality rates, the average age of these countries has risen steadily. There are already more people older than 60 than youngsters under age 15 in Europe and North America, and by 2030, nearly half the population of Western Europe will be over 50, one-quarter over 65, and 13 percent over 75.

In the United States, many people have long believed that hard work and ambition determine economic success and that this country is exceptional at promoting opportunity from the bottom up. It is the essence of the American Dream—the idea that each subsequent generation will do better than the one that came before and that together a rising tide will lift all boats. But for many, the dream is fading. The Pew Research Center has found that just 37 percent of Americans believe children today will be financially better off than their parents, a lower share than in 21 other nations in a global survey.

Millennials, welcome to adulthood. The youngest members of this generation have now put adolescence in the rear-view mirror, and their story is no longer just about what’s next; increasingly, it’s about how this adult generation is reshaping public life in the country today.

If demography is destiny, the United States—much more than its peers—is on the cusp of great change. That change is due to a deep cultural generation gap at play, which will alter all aspects of American society within the coming decade.

As people live longer, the world has a chance at a Third Demographic Dividend—improving the lives of everyone.