Once upon a time there was the Krieggspiel. A thing of great beauty, it was both expensive to acquire and cumbersome to play. Thus, the rare birds who invested time and treasure in learning the rules and acquiring the apparatus learned a great deal from the experience, the game wrought few, if any, direct effects on military institutions.
In 1876, a Prussian officer with a French name, Julius von Verdy du Vernois, published a little book called A Contribution to the Wargame (Beitrag zum Kriegsspiel.) In this modestly-titled work, Verdy (as he was known to his contemporaries) described a two-sided wargame in which the presence of an authoritative umpire allowed players to dispense entirely with rule books, tables of results, and the rolling of dice.
This approach became so popular that, nearly a century and a half after the publication of Beitrag zum Kriegsspiel, American Marines use the term “Kriegspiel” to describe an exercise of this particular type.