FILE - In this file photo dated Friday, March 29, 2019, a pro-Brexit demonstrator holds a British flag with the words

LONDON (AP) — British history has become a Brexit battleground.

British voters' decision three years ago to split from the European Union was fueled by a sense that the U.K. is fundamentally separate from its continental neighbors — a sceptered isle, rather than a European power.

Brexit-backing Conservative lawmaker Jacob Rees-Mogg has compared Brexit to historic British military victories on the continent, saying "it's Waterloo, it's Agincourt, it's Crecy." Brexit Party leader Nigel Farage fires up crowds with air-raid sirens and the theme from World War II thriller "The Great Escape."

Such patriotic messages strike a strong chord in an era of surging nationalism. But anti-Brexit politicians and historians say that view is too simplistic — and could end up making the U.K. weaker rather than stronger.

Former Prime Minister Gordon Brown argued Sunday in The Observer newspaper that "a destructive, populist, nationalist ideology" was leaving the United Kingdom "sleepwalking into oblivion."

Brown, who was Labour Party leader and British prime minister between 2007 and 2010, accused current Conservative Prime Minister Boris Johnson of "conjuring up the absurd and mendacious image of the patriotic British valiantly defying an intransigent Europe determined to turn us into a vassal state."

Richard J. Evans, professor emeritus of history at Cambridge University, lamented an increasing tendency to "talk about Europe as if it's somewhere separate, as if Britain is not part of Europe."

"I went to Gatwick Airport recently and there's a huge advertisement there for an airline that says 'Europe is closer than you think,'" he said. "And I thought, well, it's closer than you think — we're in it."

Evans said the view of Britain as an exception to the European rule ignores "the multiple connections between England and the continent over the centuries."

"If you look at our sovereigns, they have been variously French and Dutch and German," he said, noting also how culturally intertwined Britain is with continental Europe.

Like Evans, University of Toronto history professor Margaret MacMillan argues that Brexit is being "driven by a very false picture of the past" and by nostalgia for the days when Britain's empire covered a quarter of the globe.

MacMillan said many people in Britain — and especially in England, which accounts for five-sixths of the U.K. population and saw the strongest vote to leave the EU in 2016 — "are having an existential crisis about who they are."

"I think they lost their empire and lost being a major world power and they seem to have accepted that, but I think there has been a lingering sense that 'We were once great and now we're not,'" she said.

Brexit-supporting historians reject that notion, viewing the EU as an undemocratic obstacle to British sovereignty.

Cambridge University historian Robert Tombs says the fact that Britain did not experience 20th-century occupation or dictatorship sets it apart from many of its neighbors. But he thinks Britain's historical differences from the rest of Europe are often overstated, and Brexit was driven by more immediate concerns.

"We certainly had less commitment to the whole idea of European integration than countries like France or Germany," he said. "But I think attitudes to Europe are not really all that different in many EU states. And I think that has a lot to do with more recent events such as the eurozone crisis, the democratic deficit in the EU and the fact that the EU has got so much more important in people's lives and yet they have very little control over what it does."

Tombs argues that at a time of international instability, Britain is better off outside the fractious bloc.

"I think a relatively cohesive and relatively democratically governed unit is much more likely to be able to ride out whatever storms may be coming than a really rather ramshackle and unpopular and very weak confederation," he said.

Historian Andrew Roberts, a biographer of Winston Churchill, said recently that "the idea that your sovereignty effectively belongs to somebody else outside your country is just unacceptable for anybody who has any sense of British independence."

But others contend, like Brown, that Britain's democratic institutions are under threat from Brexit.

As the Oct. 31 deadline for Britain's departure from the EU approaches, the country is facing a political crisis. Johnson's Conservative government is determined to leave with or without a Brexit divorce agreement, yet Parliament will try to block him from taking Britain out of the EU without a deal. Johnson's allies have suggested he could suspend Parliament or refuse to quit if he lost a no-confidence vote, triggering a crisis for Britain's ancient but partly unwritten constitution.

Former British Foreign Secretary Malcolm Rifkind argued in a letter to The Times of London that if Johnson "sought to prevent both Parliament and the electorate having a final say on no deal, he would create the gravest constitutional crisis since the actions of Charles I led to the Civil War" in the 17th century.

That showdown ended with the monarch's execution.

Meanwhile Brexit is fraying the bonds tying together the four nations of the United Kingdom: England, Scotland, Wales and Northern Ireland.

In Scotland, which rejected separating from the U.K. in a 2014 referendum and then voted in 2016 to remain in the EU, pressure is growing for a new referendum on independence.

In Northern Ireland, which also voted to remain in the EU, the threat of a heavily guarded border with the neighboring Republic of Ireland has boosted support for a united Ireland, an idea that has historically been anathema to Northern Ireland's Protestant, pro-British Unionist majority.

"I never thought I'd hear people in Northern Ireland talking about how it might be time to reunite with the south in the way they're talking about it now," MacMillan said. "There were always fantasists who said 'One day we'll be reunited,' but you're now getting middle-of-the-road Protestants saying it.

"It's quite possible that if Brexit happens, the United Kingdom won't survive."

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Follow Jill Lawless on Twitter at http://Twitter.com/JillLawless

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Follow AP's full coverage of Brexit at: https://www.apnews.com/Brexit

Britain's Prime Minister Boris Johnson visits Pilgrim Hospital in Boston, north east England, Monday Aug. 5, 2019. Boris Johnson says he will pump an additional 1.8 billion pounds ($2.2 billion) into the National Health Service, feeding speculation he wants an early election to bolster his one-seat majority in Parliament and support for his Brexit plans. (Darren Staples/Pool via AP)
FILE - In this file photo dated Wednesday, July 24, 2019, Britain's newly installed Prime Minister Boris Johnson gestures as he speaks outside 10 Downing Street in London. The Brexit decision to split from the European Union was fuelled by a sense that the U.K. is fundamentally separate from its continental neighbours, and leading Brexit campaigner Boris Johnson once compared the EU to the conquests of Napoleon and Hitler. (AP Photo/Frank Augstein, FILE)
FILE - In this file photo dated Friday Sept. 16, 2016, Gordon Brown, United Nations Special Envoy for Global Education and former Prime Minister of the United Kingdom, holds a news conference at U.N. headquarters. The Brexit decision to split from the European Union was fuelled by a sense that the U.K. is fundamentally separate from its continental neighbours, but Gordon Brown argues that “a destructive, populist, nationalist ideology” was leaving the United Kingdom “sleepwalking into oblivion.” (AP Photo/Bebeto Matthews, FILE)
FILE - In this file photo dated Wednesday, June 19, 2019, Anti-Brexit protester Steve Bray leans in to try and see British contenders for Prime Minister at a television studio in London. The Brexit decision to split from the European Union was fuelled by a sense that the U.K. is fundamentally separate from its continental neighbours, but the future is hard to see, and both sides of the Brexit debate conjure up strong historical concepts for this sceptered isle. (AP Photo/Matt Dunham, FILE)
Britain's Chancellor of teh Exchequer Sajid Javid during a visit to the National Grid Training Centre in Newark, England, as the UK announced its GDP second quarter figures, Friday Aug. 9, 2019. Britain's  Office for National Statistics released figures showing the British economy shrank in the second quarter of 2019, as Brexit uncertainties weighed on business investment. ( Joe Giddens/PA via AP)
Chancellor of the Duchy of Lancaster Michael Gove, centre, listens, during a visit to the Port of Dover for a meeting with port officials about the work they are doing to ensure the UK's smooth exit from the European Union, in Dover, England, Wednesday, Aug.  7, 2019. (Kirsty O'Connor/PA via AP)
FILE - In this file photo dated Tuesday July 16, 2019, European Parliament members at the European Parliament in Strasbourg, eastern France.  Some people think Britain’s historical differences from the rest of Europe are often overstated, but British voters’ Brexit decision was fueled by a sense that the U.K. is fundamentally separate from its continental neighbors, rather than remaining part of a European power.(AP Photo/Jean-Francois Badias, FILE)