In the fight for racial equity, why did the spark catch here, now?

Why here? Why now?

Those questions have simmered in plenty of Minnesota minds, I'd guess, ever since the sorry Memorial Day evening when four Minneapolis cops made this state the flash point for globe-spanning outrage over racial injustice.

Why did that happen here, at the wellspring of Hubert Humphrey progressivism? Why did this spark catch fire now, more than 50 years after this state last watched an urban commercial district go up in flames during race-related unrest?

Those are the kind of questions that send an erstwhile columnist to the state demographer. Demography can't explain everything. But it usually reveals things worth knowing, I've found, especially when big questions about society start with "why." Or when thoughts turn, as they now must, to "what's next?"

For example, know this: While Minnesota remains "whiter" than many American states, it also has witnessed dramatic growth in the share of its population counted as people of color. While that growth has slowed somewhat since 2010, it hasn't stopped, and likely won't for many years to come.

"Minnesota's racial diversity has lately been increasing at about half a percentage point a year — and that's rapid for a society," state demographer Susan Brower told me last week.

Especially, I'd add, for a state in which people of color accounted for just 1.2% of the population in 1960, as the 20th-century U.S. civil rights movement gathered steam.

A big change for Minnesota came between 1990 and 2010, Brower said, when immigration brought waves of people born in Asia and Africa to the state. That took the share of Minnesotans of color from a little more than 6% in 1990 to nearly 17% in 2010.

It's at an estimated 20.4% today. That means that, much more so than during Humphrey's heyday, racial injustice is no mere abstraction in this state. The slogan "Black Lives Matter" is much more likely to be personal to Minnesotans. Barriers to the well-being of people of color are more immediately and frequently encountered. Awareness that the whole state is diminished when people of color suffer runs wider and is more keenly felt.

But so far, that awareness has not produced much narrowing of the many racial gaps Minnesotans have been hearing about for years — in household income, educational attainment, homeownership, life expectancy and the rest. Brower closely watches those metrics of inequality, and says she's been expecting to see the gaps narrow as the state population diversifies. By and large, they have not.

"We have had many people working on these issues for a long time. But the regular processes of change haven't been effective enough, or quick enough," she lamented. "Even when people at the top are sympathetic and paying attention, we're still not seeing the movement people would like to see. That's what a lot of people are reacting to now."

Instead, in some quarters (say the headquarters of the Minneapolis Police Federation), Minnesotans are seeing the resistance that rapid change in a population's racial composition can trigger. So said Brower's predecessor Tom Gillaspy, who schooled scores of journalists during 33 years as state demographer and kindly gave me a brief refresher course last week.

"Some attitudes become more entrenched in the face of changes like this," Gillaspy said. He suspects that the rural/urban and red/blue partisan divides that have seemingly widened in recent years are driven in part by disparate responses to Minnesota's changing racial composition.

But his answer to "Why now?" hearkens back to something I was taught by his predecessor as state demographer, Hazel Reinhardt: When the young adult cohort in a population becomes uncommonly large, pressure for social change spikes.

Gillaspy noted that Minnesota's population now has two outsized bumps — baby boomers and millennials, whom we boomers know as "our kids." In Minnesota, millennials overtook boomers in numbers in 2014, a few years sooner than in the nation as a whole.

Those two big cohorts may be acting in concert now as agents of social change, Gillaspy said. Not all boomers lost the idealism of their youth, he noted.

"A lot of boomers are thinking, can we make this any better? Weren't we going to have more of an effect [on eliminating racism] than we had? Meanwhile, millennials have certainly become a force, some fairly strident," he said.

They're a force capable of political impact. Brower noted that the millennial generation now ranges from 24 to 39 in age. That's full political maturity — older than were many of the boomers who marched for racial justice and an end to the Vietnam War 50 years ago.

Millennials came of age during the worst economy since the Great Depression, many of them loaded with a heavier college debt burden than any previous American generation carried. They've struggled to reach financial security, for many of them only to see paychecks lost to a virus this year. It's a situation that allows society's structural inequalities to be sorely felt.

"The movement of the millennial generation into adult roles is foundational to understanding this as a moment that's ripe for some social movement to take place. It's the foundation that helps today's movements find fertile ground," Brower said.

Thus, two demographic trends combined to propel grief, outrage and demands for change into the streets in the last four weeks. A growing population of color in Minnesota is making racial injustice real. A large young adult population is making demands for remedies urgent.

Gillaspy likened this demographic moment to an alignment of planets "that come together, then go spinning off in opposite directions. You have to take advantage of that alignment when you can, because the moment won't last."

What's next? An opportune moment has come to bend Martin Luther King's famous arc more directly toward justice. Seize that chance this year, or risk what could be many more years of watching an ever-larger share of Minnesotans — and the state itself — diminished by racism.

Lori Sturdevant is a retired Star Tribune editorial writer and columnist. She is at lsturdevant@startribune.com.