The Disunited States of America (Crosstime Traffic)

the long version

Justin's family are Time Traders. The summer before he's due to start college, he goes with them to a different Virginia, in a timeline where the American states never became a single country, and American history has consisted of a series of small wars. Despite his unease, he accompanies Randolph Brooks, another Time Trader, on a visit to the tiny upland town of Elizabeth, Virginia. He'll only be away from his parents for a few days. Beckie Royer thanks her stars that she's from California, the most prosperous and advanced country in North America. But just now she's in Virginia with her grandmother, who wants to revisit the tiny mountain town where she grew up. The only interesting thing there is a boy named Justin--and he'll be gone soon. Then war between Virginia and Ohio breaks out anew. Ohio sets a tailored virus loose on Virginia. Virginia swiftly imposes a quarantine, trapping Becky and Justin and Randolph Brooks in Elizabeth. Even Crosstime Traffic can't help. All the three of them can do is watch as plague and violence take over the town.