Throughout the 2016 U.S. presidential election, pundits and activists have debated how to get more Millennials involved in politics, always stressing their distinctive character. But it was actually this tendency to slice up the electorate into unique generations that drove young people from politics in the first place.

In the 19th century, children, youths, and adults “mingled freely together” at rowdy campaign rallies, lured by the holy trinity of booze, barbecue, and bonfire. Older citizens introduced young people to politics, helping to drive voter turnouts to their highest levels in U.S. history. “It’s the ‘big fellow,’” observed the Republicans canvassing in pool halls and saloons in the 1880s, who does the best job getting “the ‘little fellow”’ into politics.

But for the last century, American culture has isolated “the ‘little fellow.’” In schools, workplaces, and entertainment, young people have been quarantined, told that only their peers understand them. At the same time, their interest in politics has plummeted.

This is no coincidence. Dividing up the generations has made it harder for Americans to build the sustainable political engagement that once excited so many newsboys and dairy-maids.

The problem inherent in generational politics is that young people grow up. This is what makes winning their votes so difficult, and so unlike appealing to other demographics. There is little time to build networks, develop ideologies, or select leaders. With so much turnover, once a young generation gets organized politically, it’s not young anymore.

In the 19th century, older Americans worked to impart their views to younger friends, relatives, and voters. As hundreds of diaries, thousands of letters, and tens of thousands of articles in archives across the country show, politicians agreed with Abraham Lincoln’s dictum that campaigns were won by “riling up the shrewd wild boys,” and courted young people from schoolhouses to saloons. Parents raised their kids to be “born a Whig,” or feel “I am a Democrat because my father is one.”

This training began at home. Because women tended to space their pregnancies over decades, many children had much older siblings who introduced them to their preferred party. Susan Bradford, a 14-year-old Florida belle, filled her diary with tales of the multi-generational debates that shook her family’s dinner table in the 1860 election. Even her 9-year-old cousin Mattie, a budding young Whig, “shakes her golden curls and turns up her pretty little nose” in protest when her relatives sang Democratic songs.

Partisan age mixing played the greatest role in the lives of poorer young people. In Gilded Age Boston’s notorious eighth ward, scrappy Irish and Jewish kids hung around “One-Arm Pete’s” smoky tobacco shop, learning “practical politics” from their elders. For half a century, successive waves of immigrant youths inherited control of Boston’s Democratic Party through these apprenticeships.

America’s institutions forced generations to mingle. In one-room schoolhouses, 8-year-old boys and 14-year-old girls overheard 20-something students hollering partisan slogans. Such mixing, wrote an Illinois schoolteacher in 1860, proved “the genius of a republican government in which every member, male and female, large or small, feels a keen, personal interest.”

Political clubs helped blend the ages as well. These bombastic organizations stomped through America’s town squares after midnight, waving torches, hollering slogans, and riling up voters (and sometimes rioters). Most club members were in their teens and 20s, but a few veteran partisans were always hanging out, drinking ale, and discussing the best way to knock down the opposition’s marchers.

The more the ages mingled and socialized, the more politically involved the young became. For all the failures of 19th-century democracy, it did an incredible job passing down this engaged political culture.

Yet in the final years of the century, a new movement of psychologists, educators, and reformers taught that generations “should be isolated.” As families had fewer kids, and clustered pregnancies more closely together, clear generations began to emerge. Age-graded schools, reductions in child labor, and a galaxy of youth-focused entertainment—from bicycles to nickelodeons and dance-halls—allowed young people to clump together tidy groupings of their peers. Even language became more age-focused. Around 1900, Americans’ use of the terms “young” and “old” peaked in their books, newspapers, and other publications.

By 1909, the reformer Jane Addams worried that democracy “no longer stirs the blood of the American youth.” She argued that “never before have the pleasures of the young and mature become so definitely separated,” stifling the sense of a shared interest in public life.

Panicked campaigners felt this as well. Desperately trying to hold on to young supporters, the major parties created youth-only clubs, designed to recruit “beardless and boyish workers.” But without age mixing, these organizations fizzled, and turnout by first-time voters fell by more than 50 percent in the early 20th century, according to the historian Paul Kleppner.

Conventional histories often break the 20th century into a succession of discrete generations, jumping from Lost to Greatest to Silent to Boomers to Gen X to Millennials. With each generation, scholars invented new terms to discuss young people, many of which became media clichés. In the early 1900s, psychologists replaced the vague word “youths” with “adolescents,” meant to indicate a vulnerable stage during which young people needed to mature in isolation. In the years after WWII, “teenager” emerged, based on the idea that youth was not merely a phase, but an entirely separate culture, a world to be marketed to.

Americans used the word “generation” more and more across the century. If  “adolescent” and “teenager” are temporary stages, the generations became permanent identities.

The growing separation of American age groups made it difficult for young people to participate in adult politics. The two periods when Americans seemed the most fixated on generational difference, from 1900 to 1929 and 1964 to 1980, both coincided with huge drops in voter turnout. And bursts of political excitement, like during the New Deal era, were usually followed by crashes in the political engagement. The problem was that, no matter how excited a cohort might become, they just couldn’t pass down their passion to the estranged next generation.

The Baby Boomers had particular difficulty borrowing from their elders or educating their juniors. As talk of the “generation gap” peaked in 1972, voter turnout among 18-to-29-year-olds began a decades-long slide relative to turnout by those over 30 in presidential elections. Generation X continued this slump in the 1990s, although Millennials have somewhat improved youth turnout since 2004.

Millions of well-intentioned activists are working to get those Millennials voting this November. And they’re doing a good job. But America has reached peak-Millennial: This is the last presidential election in which the youngest voters will have been born before 2000. If campaigners think about politics purely in generational terms, they’ll have to start over in four years.

Generations do play an important role in American politics, giving diverse groups something to unite around. But that strength is also a weakness: uniting a generation often means isolating it, bottling up its knowledge and excitement. In politics, and in the rest of life, age mixing has a power that is often neglected in this segmented, modern world—a power that once made schoolyards brawls and dinner-table debates the centerpieces of American democracy.

This election will be over in a few months, but each new voter will have an impact for decades to come. The 18-year-olds casting their first ballots may have a say in 15 or 18 future presidential elections. Some will shape the country into the 22nd century.

So forget generations. Stop chattering about Millennials. Blurring those age-based divisions will only help make American democracy more sustainable.