It was common in the pre-modern world for the champions of rival armies to engage in head-to-head combat — hence the stories of Paris and Menelaus in Homer’s "Iliad" and David and Goliath in the Bible.
In 1520, Henry VIII of England and Francis I of France let off steam during peace negotiations at the "Field of Cloth of Gold” by having a wrestling match. (Henry lost despite his superior weight.) In 1593, King Naresuan of Thailand and Crown Prince Mingyi Swa of Burma settled a battle with a duel on their war elephants. (The king won.)
Now this practice is being revived in the very heart of the modern world: Long-time rivals Elon Musk and Mark Zuckerberg are engaged in negotiations to have a cage match, with Las Vegas and the Colosseum in Rome touted as a possible venue.