A few days after the election, the New York Times published two maps based on county-level voting data. One map showed red America, counties that went for Donald Trump: an inland nation occupying most of the land area of the United States. The other map showed blue America: a scattered archipelago consisting of the coastal corridors and inland cities that voted for Hillary Clinton. I thought of Thucydides, the Peloponnesian War, and a couple of grocery stores.

The Peloponnesian War pitted two ancient Greek city-states, Athens and Sparta, each with its allies, in a war that lasted from 431 BC until Athens’ defeat in 404. Sparta was an inland power and depended on its unmatched hoplite soldiers and its power over the central Greek land mass. Athens controlled an empire of islands and relied on its navy and a steady stream of tribute from its allies. Because Thucydides, the historian of that war, wrote a classic study of geopolitical rivalry that is still studied at the United States Naval War College and elsewhere, it’s easy to think of Athens and Sparta as different nations, like the United States and China; in fact, two separate articles about China in the December 2016 issue of The Atlantic are far from the first to invoke the “Thucydides trap” to describe the way that a rising power inevitably comes into conflict with one that is already established.

Thucydides himself, though, makes it clear that understanding the war between Athens and Sparta meant understanding not only national interests and anxieties, but also different forms of a common Greek culture. Athenians and Spartans were both Greek: they spoke the same language, worshipped the same gods, shared a national literature and a foundational text, Homer, and met at common festivals. In the negotiations leading up to the war, Thucydides has a third party, a Corinthian ambassador, describe for the Spartans the ways in which their character and world view differ from the Athenians’. Those differences had as much to do with the war as Spartan anxieties about Athenian power or Athenian need for a maritime empire.

Thucydides makes me want to ask, are we one country? One polis, as the Greeks might have put it? One culture, as the Athenians and Spartans were? Trump voters are not Spartans, and Clinton supporters are a long way from being Athenians. As President Obama among others likes to remind us, we are all Americans, just as the Athenians and Spartans were all Hellenes. We speak versions of a common language and enjoy common festivals (thank you, Thanksgiving and Super Bowl Sunday). But in the 2016 election, Trump won 76 percent of the counties that have a Cracker Barrel and only 22 percent of those that have a Whole Foods. The gap in political views between organic shoppers and nostalgia seekers has grown steadily since 1992, according to Dave Wasserman of the Cook Political Report, and it hit 54% this year.

That food fight may reflect a more significant statistic: as the Brookings Institution reported, the roughly 500 counties that Clinton won accounted for 64 percent of U.S. economic activity in 2015, while the more than 2,600 that Trump won accounted for only 36 percent. This disparity is only one example of fractures in a common culture that is beginning to divide along lines drawn by income, education, and zip code. At the end of the first book of his history, Thucydides reports a speech by Pericles to the Athenian people. The coming war, he explains, will be decided by money: the Athenians’ wealth, and the Spartans’ lack of it.

I don’t see war between the people of the coasts and the people of the mountains and plains in America’s future—but like Athens and Sparta, we are growing farther apart as our interests diverge, and our common civic culture is in danger. We can and should be a diverse nation in which many cultures co-exist, but ironically, diversity only works if people can talk with one another; if, that is, they have some overarching civic culture in common. Otherwise it’s divergence, not diversity. It is not enough to share the same Constitution and laws. It’s time to read the same books. The first book of Thucydides might be a place to start—it analyzes the way in which Athens and Sparta went from close allies joined in a common cause to open enemies in the space of fifty years. Maybe it’s also time to sit down for a meal catered jointly by Whole Foods and Cracker Barrel.