On 14 November 1916, Robert Jackson, an American relief volunteer in Belgium, checked out disturbing rumors. The German occupiers of Belgium, he had heard, were deporting workers to serve the German war effort, breaking official promises and violating international law. The latest “selection” would take place at Court-St.-Étienne, sixteen miles southeast of Brussels, at an empty textile mill.

“In the distance,” Jackson later told his journal, “the can[n]on were booming very loud, the 3rd day in succession,” as a “long serpentine of men” filed into the mill. Outside, “entirely apart & away were the masses of women & children waiting & weeping, wondering whether their men would be taken & coming as near as was permitted.”

If a man was told “to the left,” that meant liberty–“so far as liberty exists for the inhabitants of Belgium”–and “to the right” meant Germany. The “selection” screened thousands of men in four hours, of whom almost nine hundred were loaded onto sealed boxcars, bound for Germany. There, they would be offered contracts to work in war plants and tortured if they refused.

That same day, American newspapers reported a protest by Cardinal Désiré Mercier, the chief Catholic prelate in Belgium. Many neutral nations also criticized the German policy, even Switzerland, but not the United States. President Woodrow Wilson, having just narrowly won reelection under the slogan, “He Kept Us Out of War,” refused to speak publicly on the matter; he interpreted neutrality to mean diplomatic silence, except when he felt American interests were involved. (He also hoped to mediate peace, a delusion the Germans encouraged, but that’s another story.)

In 2003, I read Robert Jackson’s journal at the Hoover Archives at Stanford; Herbert Hoover directed the relief effort that employed Jackson, and many of its papers wound up there. When I opened the journal, a small, hard-backed notebook like those used for school compositions, my hands trembled. The ink had browned with age but was generally legible, and the words leaped off the pages, evoking passions and images of people long dead. This was the eyewitness account I was looking for, a description that would retrieve a speck of history from obscurity: the deportation of 120,000 Belgians in 1916-17, a little-known event in a great war. I used it in my book, The Rape of Belgium, and it has stayed with me ever since.