In the eighth and final season of “Homeland,” the C.I.A. officer Carrie Mathison (Claire Danes) returns to Afghanistan and comes across the child of a contact she dealt with years ago. He’s growing tall now. When she last saw him, he barely came up to her knee.

“Homeland,” which returns Sunday night on Showtime, is about a lot of things, personal and geopolitical. But at its most powerful, the new season conjures that simple, sad feeling: My God, it’s been so long. All of this — the war, the fear, the vengeance — has been with us for so many years, it’s hard to remember a time without it.

That feeling was built into “Homeland.” It began, in 2011, a full decade since the Sept. 11 attacks. “24” — the show’s precursor, with which “Homeland” shares creative talent — had by then aired eight seasons.

Where “24” flourished in the fight-or-flight rush of 9/11’s aftermath, spinning out cathartic fantasies of ever-bigger terrorist attacks on the United States, “Homeland” looked at the psychic cost of all those years of fighting and catastrophizing.