Read: Millennials didn’t kill the economy. The economy killed Millennials.

Zoning codes in America have their roots in the early 1900s. Some land-use rules arose out of efforts to manage growing density in cities due to industrialization and new construction technologies that allowed taller buildings. But most zoning was intended to protect property values for homeowners, or to exclude certain racial groups. For many decades, though, zoning codes were relatively limited in scope.

Stricter zoning rules began to be implemented in many places in the 1940s and 1950s as suburbanization began. But then things got worse in the 1960s to 1980s. This shift is reflected in the increasing frequency with which various land-use associated words were used in Google’s database of American English-language publications. These decades, when the political power of the Baby Boomer generation was rapidly rising, saw a sharp escalation in land-use rules.

There’s debate about why this is: Some researchers say the end of formal segregation may have pushed some voters to look for informal methods of enforcing segregation. Others suggest that a change in financial returns to different classes of investment caused homeowners to become more protective of their asset values.

Today, strict land-use rules—whether framed as rules about parking, green space, height limits, neighborhood aesthetics, or historic preservation—make new construction difficult. Even as the American population has doubled since the 1940s, it has gotten more and more legally challenging to build houses. The result is that younger Americans are locked out of suitable housing. And as I’ve argued previously, when young people have to rent or live in more crowded housing, they tend to postpone the major personal events marking transformation into settled adulthood, such as marriage and childbearing.

But, of course, Boomers didn’t only make rules that nudge young people out of homeownership. They also made new rules restricting young people’s employment. Laws and rules requiring workers to have special licenses, degrees, or certificates to work have proliferated over the past few decades. And while much of this rise came before Boomers were politically active, instead of reversing the trend, they extended it.

Just as tight land-use rules make existing homeowners richer by reducing how many new houses are listed on the market, strict licensing rules make existing workers richer by reducing competition in their fields. And while some industries clearly need licensing rules for health and safety reasons, most of the growth in licensure has been in fields where health and safety justifications are less salient: Do you really need hours of course work and special exams to be a florist, an interior designer, or an auctioneer?