Travel guides can tell you a lot about a country. But locals often have stories and facts you won’t find anywhere else.

On the Western Front, a dead German artilleryman and several draft horses, ca. 1918. Exact figures are hard to come by, but an estimated 8 million horses died during the four years of war.

The Black Tom bombing, along with Germany’s unrestricted submarine warfare and the Zimmerman Telegram, eventually led to ...