The German post offices abroad were a network of post offices in foreign countries established by Germany to provide mail service where the local services were deemed unsafe or unreliable. They were generally set up in cities with some sort of German commercial interest. In early use only the cancellation mark can identify their postal use abroad; such stamps are known as "Vorläufer" (forerunner) stamps. Later stamps are identified by overprints even when not postally used. German abroad stamps started appearing in the late 19th century and reached their heyday at the beginning of the 20th century; they closed down during or shortly after World War I.