Tucking into a dish of Scottish haggis is not a task for the fainthearted. There are various haggis recipes, but basically it is sheep’s pluck – the heart, lungs and liver – cooked together, then mixed with suet and oatmeal and boiled in a sheep’s stomach, then served, sometimes drenched with Scotch. People who pour whisky on oatmeal are not shrinking violets. Remember this on Thursday when Scotland votes on independence from the United Kingdom.

There are economic reasons for and (mostly) against Scotland disassociating from the queen’s realm. This issue, however, touches chords of memory more interesting than money.

In “The Long Shadow: The Legacies of the Great War in the Twentieth Century,” Cambridge University historian David Reynolds notes that World War I, a breaker of empires and maker of nations, quickened interest in nationalism and the nature of nationhood, especially the distinction between a civic nation and an ethnic nation: The former is “a community of laws, institutions, and citizenship,” whereas an ethnic nation is “a community of shared descent, rooted in language, ethnicity, and culture.” France embodied civic nationalism, forged by its revolution; Germany, “steeped in Romantic conceptions of the Volk,” exemplified ethnic nationalism.

The United States is a civic nation because it is a creedal nation – founded, as Jefferson said, on “truths” deemed “self-evident,” and dedicated, as Lincoln said, to a “proposition” (that all are created equal). Scotland is largely an ethnic nation, and whether Scots opt for or against independence, the continued vitality of their national sentiments testifies to the ability of differences to resist homogenization by the commercial and cultural forces of modernity.

Even after its parliament was dissolved in 1707, Reynolds writes, Scotland retained its separate educational and legal systems and an established Presbyterian church. Reynolds says that “to subsume conflicting ethnicities” and foster national unity among Britain’s components – the English (three-quarters of the U.K.‘s 1910 population), Welsh, Irish and Scots – an ideology of “Britishness” was cultivated by means such as the cult of Lord Nelson, and adoption of “God Save the King” as the national anthem.

But by the end of the 19th century, Reynolds says, there was a “backlash against Britishness.” In Scotland, the poet Robert Burns and the medieval warrior William Wallace became cult figures, and in May 1913 a Scottish home rule bill was introduced in the House of Commons. Then the war came.

And what Reynolds calls “the crisis of Britishness” receded. Scotland boomed (its coal, steel and shipbuilding) and bled: It had, Reynolds says, the U.K.’s “highest rate of army volunteering” – one in six British soldiers was a Scot – and “the highest death rate among those who enlisted.” The war that followed the war to end war kept Scottish nationalism tamped down. “Only from the late 1960s,” writes Reynolds, “when Germany was no longer a threat, did the English Other become a bogey again and Scottish and Welsh nationalism start to revive as serious political movements.”

The 19th was a century of national consolidations – in the United States, Italy (the Risorgimento under Cavour), Germany (Bismarck hammered together numerous principalities and other entities) and Belgium, which was invented from various odds and ends. The 20th century, however, brought the breakup of empires – the British, Austro-Hungarian, Ottoman, Russian and then Soviet empires. The disintegrative impulse continues in, among other places, Spain, where Catalonians are asserting their particularities as Basques have long done.

Were Scotland now to become a sovereign nation, as it was until 1603, it would have a GDP ranking 16th among what would then be the 29 nations of the European Union (just behind Ireland and ahead of the Czech Republic) and would be the 20th-most populous. And the United Kingdom would have to redesign its flag, the Union Jack.

It is a composite of three crosses of the nations united under one sovereign – Scotland, Ireland (since 1921, Northern Ireland) and the united kingdoms of England and Wales. The cross of St. George, England’s patron saint (the Catholic Church has demoted him, perhaps partly because of doubts about the dragon slaying), is a red cross on a white ground. The cross of St. Patrick, Ireland’s patron saint, is a diagonal red cross on a white ground. The cross of St. Andrew, Scotland’s patron saint, is a diagonal white cross on a blue ground.

Scotland’s Royal Arms banner, emblazoned with a lion rampant, flies over Balmoral Castle when the queen is not there. Which means it could be used even more after Thursday.

© 2014, Washington Post Writers Group