The newlyweds moved to Germany, where van Loon received his Ph.D. from the University of Munich in 1911 with a dissertation that became his first book, The Fall of the Dutch Republic (1913).

His most famous pet was named Mungo, after Sir Walter Scott's dog, grew too large to handle and was sent back to Newfoundland where he was adopted as a mascot by Lieut.

Mungo was photographed on base with Charlie McCarthy and Edgar Bergen, and flew onboard missions seeking to bomb Nazi U-boats during World War II.

As a writer he was known for emphasizing crucial historical events and giving a full picture of individual characters, as well as the role of the arts in history.

[15] In the summer of 1938, during an extended visit to Scandinavia, Van Loon met with refugees who had recently fled Nazi Germany and who gave him first-hand accounts of the terror that they had experienced.