After 43 years in the European Union, the British people were asked for the first time whether they wanted to be there. Narrowly, they said no.

The country had gone mad, said half the voters; it had regained its senses, said the rest. Britain had betrayed its best friends, said those who wanted to stay; it had avenged a betrayal, replied those who wanted to go. Brexit had ruined Britain’s economy, or perhaps it had freed it. It was the best of times; it was the worst of times. The only thing everyone agreed on was that Brexit was unprecedented.

But it wasn’t. Writing my new book, Geography Is Destiny: Britain and the World: A 10,000-Year History, taught me two big things. I’ll get to the second in a moment, but here is the first: Brexit was nothing more than the latest round in an argument as old as the British Isles themselves.

Ever since the end of the Ice Age, when rising sea levels filled the English Channel with water, two geographical facts have governed British history. First, that the Isles are (obviously) islands; and second, that they are close to the Continent (only 21 miles from Calais).

As far back as we can see, Britons have been arguing over which fact matters more. The archaeological record suggests that this disagreement goes all the way back to the hunter-gatherers in Britain at the end of the Ice Age, and it continues in our own days.

In the oldest surviving account of British identity, written nearly 2,000 years ago, the Roman historian Tacitus tells us that some Britons embraced Rome’s wealth and cosmopolitanism. “The toga was everywhere to be seen,” he says—before adding that while Britons who rejoiced in proximity to the Continent “spoke of such novelties as ‘civilization,’” those who preferred insularity thought “they were only a feature of enslavement.”

In the 21st century as much as in the 1st, Britons who embrace a wider world tend to think their own views are broad and enlightened while their opponents’ are narrow and ignorant; those who prefer the local to the global see themselves as broad and democratic and their opponents as narrow and elitist. When Brexiteer politician Michael Gove told an interviewer in 2016 that “people in this country have had enough of experts,” he was speaking from a script written millennia earlier.

The archaeological record suggests that the disagreement over Brexit goes all the way back to the hunter-gatherers in Britain at the end of the Ice Age.

There is nothing to be surprised at in the closeness of the Brexit vote, 48 percent to stay and 52 percent to go. This 10,000-year debate has always been a close call. No one went mad in 2016; Brexit was not a crime. But it might have been a mistake, which brings me to the second big thing I learned writing this book.

The fundamental facts of Britain’s geography have persisted for 10,000 years, but right now geography is changing its meanings faster than ever before. Technology is shrinking the world; insularity means little; everywhere has become proximate to everywhere else. Not even the U.S., behind its two vast oceans, is secure anymore. For the British, the English Channel has effectively ceased to matter, because the 21st century isn’t going to be about Brussels. It’s going to be about Beijing.

The Brexit brouhaha missed what the maps now mean. Everyone in the West needs to wake up to the emerging facts of a new, globalized world—because geography is destiny, but it’s up to us to decide what to do about it.

Ian Morris is a British historian and archaeologist and a professor of classics at Stanford University. His new book, Geography Is Destiny: Britain and the World: A 10,000-Year History, is out now from Farrar, Straus and Giroux