How smart are the robots getting?

Franz Broseph seemed like any other Diplomacy player to Claes de Graaff. The handle was a joke - Austrian Emperor Franz Joseph I reborn as an online bro - but that was the kind of humor that people who play Diplomacy tend to enjoy. The game is a classic, beloved by the likes of John F. Kennedy and Henry Kissinger, combining military strategy with political intrigue as it re-creates the First World War: Players negotiate with allies, enemies and everyone in between as they plan how their armies will move across 20th-century Europe.

When Franz Broseph joined a 20-player online tournament at the end of August, he wooed other players, lying to them and ultimately betraying them. He finished in first place.

De Graaff, a chemist living in the Netherlands, finished fifth. He had spent nearly 10 years playing Diplomacy, both online and at face-to-face tournaments across the...