The conventional wisdom about today's young voters is that they're inherently unreliable and therefore have earned the lack of courtship from politicians.

It is true millennials are significantly less likely to vote than their counterparts were in the 1980s or the first wave of postwar baby boomers in the mid-60s. Moreover, today's older generations have become substantially more engaged over the decades.

But it wasn't always this way, said Jon Grinspan, author and historian at the Smithsonian’s National Museum of American History. Throughout the 19th century, young people voted en masse in wild and spectacular fashion, and were by far the most coveted demographic in politics.

In his book, "The Virgin Vote: How Young Americans Made Democracy Social, Politics Personal, and Voting Popular in the Nineteenth Century," Grinspan puts together a glimpse of the political engagement of children and the party bosses who relied on them by drawing on hundreds of diaries and letters of young Americans of various socioeconomic backgrounds between the years 1840 and 1900.

"People know the names to some of these presidents and maybe some of these elections, but they know very little about the on-the-ground life of American democracy," he said. "And as I read these diaries of young people living in Wisconsin, or upstate New York, or Florida, there's just this whole political world that was really relevant to 15-year-olds that I wanted to study and understand more."

Those teenage worlds, said Grinspan, involved showing up at rowdy rallies, wild one-room schools and raucous salons – all of them a nexus to partisan politics as it was absolutely central to life back then. ...