“Golden Age” by Jane Smiley; (Knopf, 384 pages, $26.95)

The question comes late in the final installment of Jane Smiley’s “Last Hundred Years” trilogy: “Do you think that we’ve lived through a golden age?”

“Why would we think that? No one thinks that,” is the immediate reply, from a sleepy aunt who doesn’t care to ponder the mysteries of fate and history. But Smiley’s answer in the greater context of this sprawling, multigenerational American saga is more thoughtful, more complex. In “Golden Age,” she wraps up what she launched in “Some Luck” and “Early Warning”: the ambitious, absorbing story of the Langdons, an Iowa farm family with branches stretching to California and Chicago and New Jersey and Washington, D.C.

The second generation of Langdons — Frank, Joe, Henry and Claire — has grown into late middle age. Frank, always aloof, reconnects emotionally and physically with his wife Andy, whose ethereal qualities make her easy to underestimate (you would be foolish to do so). Their grown daughter Janet, who loathes her father, finds solace in her children and horses, and their twin sons, Michael and Richie are still warring in different ways.

Joe has passed the Langdon farm onto his son Jesse, who finds none of his children are interested in farming, though the boys will join the military, providing Smiley an avenue into the subject of war and its emotional costs. Henry, ever the scholar, remains close with Claire, the youngest, who has forged a new career and made a better marriage than her first with a quiet man named Carl.

It falls to sunny Charlie, grandson of Arthur and Lillian, to unite the far-flung family members, and he manages at times. But a strong streak of pessimism runs through “Golden Age”: Jesse’s wife Jen may believe that “everything would work out because it always had,” but Smiley does not. Among her fears: economic inequality, climate change, violence, racism and radical changes in America’s food sources. Smiley lays out the dangers unemotionally, daring us to ignore them at our own peril.

But “Golden Age” is not a polemic, nor is it entirely downbeat. Claire, in that hotel room more fully considering Janet’s question about a golden age, puts our existence into perspective: “(S)he did think right then that all golden ages, perhaps, were discovered within. No one would ever know that her father, Carl, the endless Iowa horizon, a pan of shortbread emerging from the oven, and her grandchildren laughing in the next room had indeed made her life a golden age.” In the wild, unpredictable, precious ride of life, we can still find moments to savor.