Good question!

The Führerreise ("Leader's Ride") and Kriegsspiele ("War Games") were pillars of the Prussian (later German) war planning and professional development process. At the Prussian Kriegsakademie and the Großer Generalstab ("Great General Staff"), future leaders and staff officers underwent staff rides and war games to expose them to the problems, enemy tactics, and terrain they'd face in an actual war.

Now, these concepts weren't new. War games (or at least games about war) have been around for millennia. Officers had visited old battlefields and potential battlefields for centuries. For example, in the summer of 1814, Wellington had visited the Waterloo area to scout out the area as a potential battlefield. In June 1815, he'd put his knowledge of the ground to good use to defeat Napoleon during the climactic battle.

Some of Prussia's greatest 18th century military leaders had begun their military careers re-treading old battlefields and re-reading old campaigns, as David Ian Hall writes:

Even at age 22, then an inexperienced and un-blooded Colonel, Frederick [(later Frederick the Great)] appreciated how essential professional education was to an effective and efficient army. He was, after all, not only the Crown Prince of Prussia but also a willing child of the Enlightenment. Frederick read the history of his predecessors, of the rulers and the armies of Prussia. He analyzed their successes and failures and identified the reasons for them. He also conducted personal battlefield tours and tactical walks, searching out old veterans who could describe to him the battles that they had fought. Further encouragement for these activities came from his father, King Frederick William, and Commander-in-Chief of the Imperial Armies, Prince Eugen of Savoy. One a number of occasions, Eugen advised the young Frederick to "read military history ... to meditate unceasingly on your profession and on the operation of great generals ... and always to keep the great objectives and on the operations of great generals ... and always to keep the great objectives of a campaign in view." The pupil heeded the instruction of his tutor...

Wargaming likewise had a long tradition in Germany. As a side note, if you're interested in reading more about German Kriegsspiele, "German War Gaming" by Milan Vego goes into the subject in great detail.

As early as the 1600s there were variants of chess like Das Schackoder Koenig-Spiel ("King’s Game") and the more militaristic Neu-erfundenes grosses Koenig-Spiel ("Newly Invented Great King’s Game"). Milan Vego says these Spiele were just fun and games; they were "designed to serve not only as a pastime but also as a means of studying the military and political principles of the time." In 1780, courtier Dr. Johann Christian Ludwig Helwig created his own Koenigspiel on a multi-colored chessboard with 1,666 squares of various colors. Each color was a different type of terrain (mountains, swamps, forests, water, villages, etc.). In keeping with it's militaristic theme, the board was divided down the middle by a "frontier." Vego also comments on the militaristic nature of this game, as it "was meant to encourage young noblemen to think about important military questions and to teach them basic elements of military art and science." The Koenigspiel caught on in Germany and was also picked up by French, Austrian, and Italian military officers.

In 1797, military theoretist Georg Venturini, invented the Neue Kriegsspiel (“New War Game”). This game was more realistic and even more militaristic. The board was actual territory between France and Belgium. Moves were limited by the actual distance marching troops could cover. Moves made in "winter" were slower. The complexities of logistics and reinforcements had their own 60-page rulebook. A player who failed to provision his "men" would suffer penalties. This comprehensive, if unwieldy game also became popular in Germany, France, Austria, and Italy.

In 1811, Prussian Georg Leopold Baron von Reisswitz made an even bigger wargame. Set on a 1:2,373 scale sand table, his Anleitung zu einer mechanischen Vorrichtung um taktische Manoevers sinnlich darzustellen ("Introduction to a Mechanical Gadget to Sensory Depiction of the Tactical Maneuver") was big in every way. It could take up to ten players on each side, with neither side aware of the other's moves. An umpire helped coordinate this tactical circus.

In 1824, Lieutenant Georg Heinrich Rudolph Johann von Reisswitz, further improved the game with his Anleitung zur Darstellung militaerischer Manoever mit dem Apparat des Kriegs-spiels ("Instruction for Representation of Military Maneuvers under the Guise of a War Game"). The younger von Reisswitz's variation used a 1:8,000 topographical map and simulated forces as small as a battalion or as large an army corps. The process of playing the game closely mirrored actual staff work and "emphasized the importance of general-staff officers," as Vego notes.

The umpires were responsible also for devising a realistic and interesting initial situation. They would present a “general idea” or “outline” of the situation (in modern terms, a scenario) to the players indicating the positions of the main body of troops of both sides and giving reasons for players to conduct moves on the board. If there was more than a single player on each side, one would be commander in chief and the other the commander of a major part of the force, such as the main body or vanguard. A commander would submit a written plan to the umpire containing the intended maneuver, orders to individual units, orders given to other players, the intended final position of troops, etc. Reisswitz quantified the effects of combat, so that results of engagements were precisely calculated rather than debated.

The game was a smash hit in Prussia!

General Karl von Mueffling (1775–1851), chief of the general staff (1821–29) in Prussia, exclaimed, “It’s not a game at all! It’s training for war. I shall recommend it enthusiastically to the whole army.” He fulfilled that promise: a royal decree directed every regiment in the Prussian army to play the game regularly. By the end of the 1820s each Prussian regiment was purchasing with state funds materials for war gaming ... Numerous war-gaming clubs sprang up in Germany. In 1828, Helmuth von Moltke, Sr. (1800–91, later a field marshal), joined such a club.

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