In the summer of 1914, Europe had been at peace. If France had been watching her neighbor Germany with alarm, as Germany’s army and navy swelled, she had not been idle. Indeed, her battle plan if hostilities with Germany ever resumed was to race eastward and recapture Alsace-Lorraine. Attack: that was the word, and the inspiration. Attack and avenge the honor of France. But so far, the tense peace of Europe, held together by her complex network of alliances, had remained unbroken.

And then, out of the blue, an Austrian archduke was murdered in Sarajevo. What had this to do with Germany and France? On the face of it, nothing. But when Austria declared war on the Serbs, Russia defended their fellow Slavs. Germany, allied with Austria, was obliged to declare war on Russia. Russia was allied with France. To avoid a war on two fronts, Germany resolved to smash France quickly. The German High Command already had a detailed blueprint, the Schlieffen Plan, for how to do it.

Would not this bring out the army of the huge British Empire to defend France, to whom she was bound by the Entente Cordiale? Perhaps. But the Entente was rather vague about hostilities. The British might fight, or they might not.

Except for one thing.

Little Belgium. Set up when Europe was being reorganized after the fall of Napoléon. A constitutional monarchy with a modest king and queen. A small, comfortable kingdom, whose neutrality was universally recognized as inviolable by all the countries of Europe.

The large French forces, poised to attack, lay south of the Belgian border. The German army had no wish to go up against them. But if the German army crossed Belgium, it could walk straight into France unhindered. Diplomatically it was impossible. Morally unthinkable. Militarily, obvious.

In August the Belgian king and his government received a note from Germany. It was couched in the most diplomatic terms. But its message in plain English was clear as day:

We’re going to need to walk through your country and occupy it for a while. When we’re done, you can have it back again. Hope you don’t mind. We’ll be coming in a couple of days.

But the Belgians did mind. They said they’d fight. It had not occurred to the German High Command that this comfortable little kingdom would be so valiant.

And Britain had a treaty with Belgium. A cast-iron treaty, to defend it if Belgium was attacked. Britain, therefore, entered the war at once.

Thus, in the first days of August 1914, all the tottering structures erected to preserve the peace of old Europe came crashing down. No one could have foreseen that it would happen this way.

By the first days of September, Thomas Gascon was in a quandary. Though delayed by the tough Belgian resistance, the German army was in France, its advance guard less than fifty miles from Paris. And every Parisian knew what that meant.