The same is true, more subtly, of Emily St. John Mandel’s “Exit Party.” St. John Mandel wrote gorgeously about a postapocalyptic world in “Station Eleven,” her 2014 book about a civilization unraveled by a pandemic. Given that book’s prescience, it’s a little unnerving that she has now written about civil war. “The United States had come undone following a coup d’état,” she tells us on the first page. The story begins with a party in Los Angeles to celebrate the lifting of a curfew in the newly independent California Republic.

St. John Mandel’s post-civil-war America is a brutal place. Los Angeles is full of shantytowns and refugees. In the middle of America, we soon learn, things are worse, as rival militias scrap over territory. Still, there’s hope in the new configuration. “I know countries don’t last forever, and there’s always going to be new ones,” says a guest at the party, “but it feels like a miracle, right?”

During the first Trump term, people often said they felt we’d veered onto a bad timeline. “Exit Party” dramatizes that notion, and as the book goes on, it starts to seem that the timeline in which America cracks apart might not be the worst one. “There was a world where my homeland had fractured into disarray, and another where my homeland had closed like a fist,” says one character.

Our constitutional system protects us from each other, but its rigidity — the near impossibility of passing constitutional amendments, the structural bias against cities — has also come to feel like a cage. “The Breakup” and “Exit Party” suggest that it’s easier to imagine a future full of possibility outside this system than in it. “It does seem like people are getting increasingly impatient, and I think the novelists are picking up on that,” Richard Kreitner, the author of “Break It Up: Secession, Division and the Secret History of America’s Imperfect Union,” told me.

Kreitner pointed out that stories of disunion proliferated during other moments of national strife. He wrote in Slate that years before the Civil War, Southerners wrote novels about secession and sectional bloodshed. Amid the upheavals of the 1970s, there was another spate of books imagining the end of the United States, including “Ecotopia,” about a breakaway West Coast environmental paradise, and the white supremacist “The Turner Diaries,” which continues to inspire the far right.