Last time I was in Paris, with my son, we walked down to see the Louvre on a Tuesday afternoon, forgetting that it’s always closed on Tuesdays. So instead we took a long walk up the Champs Elysées to the Arc de Triomphe.

The day must have been some EU anniversary, or else it coincided with a visit from a Berlin dignitary. All up the broad avenue, flags fluttered from every post: the French tricolor and the red-yellow-black ensign of Germany. It was somewhat daunting to see this display of Franco-German unity, in the year of world defiance of America, and feel our small and American selves beneath it.

At the end of our long walk, we reached the Arc. We stood under it and looked up and around, and read what was engraved in marble and cast in bronze.

The grand monument was commissioned by Napoleon in 1806, the year he crushed Prussia at Jena-Auerstedt.

A big marker right underneath the arch celebrates the glorious day in 1918 when France recovered Alsace-Lorraine, the two provinces taken by Germany as spoils of victory in 1870, whose loss haunted and inspired a generation of Frenchmen. Somehow the modern French guides to the site overlook this big sheet of metal, though some prattle instead about “European unity.”

That memory came back to me this week, after reading Michael Totten’s piece about the myth of the unity of the West.

The roundabout that circles the arc — the Place de l’Etoile — is said to be so notorious for traffic accidents that no insurance company will put up coverage for any vehicle that routinely drives through it. Given the history of European nations, I’d be more inclined to insure such a car than I would to bet on lasting unity.

Like divorced couples, these countries have a history with one another we Americans can only faintly understand. But not only have the European nations achieved and maintained their independence in spite of one another, they’re like old prizefighters who literally have been shaped by the blows they have dealt one another.

In the 1790s France gradually conquered western (non-Prussian) Germany. German patriots and Francophobes like Ernst Moritz Arndt called on their fellow Germans to learn from republican institutions and virtues of France.

After Jena-Auerstedt, Prussia suffered an ignoble collapse and capitulation to Napoleon, The Prussians plunged into crisis and eventually reformed their state on the French model. Clausewitz witnessed this cataclysm and wrote about it.

The French, secure in the evidence that their neighbors were an inferior people (and that Napoleon, not France, had been beaten in 1815, and anyway it has taken a coalition of the whole of Europe to do it), saw themselves as loving protectors of the little non-Prussian German states along the Rhine against the terreur prussienne. It shaped their foreign policy, and Paris helped keep Germany weak and divided for decades

Then came the disaster of 1870, when France not only saw a united Germany rise under Prussian rule, but it also endured a stinging defeat by the Prussian military, with the loss of the two cherished provinces.

Now it was France’s turn to learn. Frenchmen marveled at the geographical knowledge of the invading German soldiers. “When they asked for directions the question was never, ‘Where does this road go?’ but rather ‘Isn’t this the road to …?’ And they never got lost.” The Germans, for their part, were astonished that even some of the French officers they captured were illiterate.

And so French educational reform began in the 1880s. Of course, when one said “Germany” one also meant one’s domestic enemies. The new republican educational system of the 1880s also was an expression of anti-Catholic assertiveness in the age-old struggle of the red and the black. But that, too, is part of the tale of influence through conflict.

The arc became a symbol again of France’s thirst for revanche — the recovery of the lost provinces — in May 1885 when the body of Victor Hugo, the furious revanchist, lay in state under the Arc de Triomphe and more than a million people came to pay their respects. Then in 1914, the day dawned that the revanchists had awaited for two generations. It was a day out of Hell.

The day the Battle of Verdun started in 1916, the sword carried by the figure representing the Republic [on the Arc] broke off. The relief was immediately hidden to conceal the accident and avoid any undesired associations or interpretations as a bad omen.

Germany lost. Alsace and Lorraine returned to France, as the Arc commemorates. Just a few feet from that commemoration is the body of an unknown soldier, buried under the Arc to symbolize his 1.5 million peers who died in that war.

Hitler, weaving his web of power in Germany, praised the French republican resistance that put up another fight after the empire’s army had failed in 1870 — a doomed popular battle that preserved Franch honor, even if it costs tens of thousands more lives and ended in the dabacle of the Paris commune. In a speech of Sept. 12, 1923, shortly before the Munich putsch, Hitler contrasted this to the Weimar republic.

“The will to defend the state created the French republic in 1870. It was a symbol not of dishonor but of the upstanding will to preserve the nation. French national honor was revived by the Third Republic. What a contrast to our republic!”

On June 14, 1940, when German attacks had smashed France’s defense and forced the French government to give up the city lest it be destroyed, German Gen. von Bock, commander of Army Group B, flew into Paris and headed for the Arc de Triomphe, there to salute the first German combat troops to parade into the capital.

And on and on. There had been turns of French good will toward Germany in all that — very temporary ones, usually when some fresh insult wafted across from Britain. But history doesn’t end. The flags we saw all down the Champs Elysées that October day would be furled and gone within a week. The marble arch will endure for centuries.