Wargame
Venturini's game was played on an even larger grid. Venturini's game also added rules governing logistics, such as supply convoys and mobile bakeries, and the effects of weather and seasons, making this perhaps the first operational-level wargame. In 1806, an Austrian named Johann Ferdinand Opiz developed a wargame aimed at both civilian and military markets. Like Hellwig's game, it used a modular grid-based board. But unlike Hellwig's game, Opiz's game used dice rolls to simulate the unpredictability of real warfare. This innovation was controversial at the time. Hellwig, who designed his wargame for both leisure as well as instruction, felt that introducing chance would spoil the fun.
A criticism of the chess-like wargames of Hellwig, Venturini, and Opiz was that the pieces were constrained to move across a grid in chess-like fashion. Only a single piece could occupy a square, even if that square represented a square mile; and the pieces had to move square by square, their exact location within a square being immaterial. The grid also forced the terrain into unnatural forms, such as rivers that flowed in straight lines and bent at right angles. This lack of realism meant that no army took these wargames seriously.

Kriegsspiel (1824): In 1824, a Prussian army officer named Georg Heinrich Rudolf Johann von Reisswitz presented to the Prussian General Staff a highly realistic wargame that he and his father had developed over the years. Instead of a chess-like grid, this game was played on accurate paper maps of the kind the Prussian army used. This allowed the game to model terrain naturally and better simulate battles in real locations. The pieces could be moved across the map in a free-form manner, subject to terrain obstacles. The pieces, each of which represented some kind of army unit (an infantry battalion, a cavalry squadron, etc.), were little rectangular blocks made of lead. The pieces were painted either red or blue to indicate the faction it belonged to. The blue pieces were used to represent the Prussian army and red was used to represent some foreign enemy—since then it has been the convention in military wargaming to use blue to represent the faction to which the players actually belong to. The game used dice to add a degree of randomness to combat. The scale of the map was 1:8000 and the pieces were made to the same proportions as the units they represented, such that each piece occupied the same relative space on the map as the corresponding unit did on the battlefield.
The game modeled the capabilities of the units realistically using data gathered by the Prussian army during the Napoleonic Wars. Reisswitz's manual provided tables that listed how far each unit type could move in a round according to the terrain it was crossing and whether it was marching, running, galloping, etc.; and accordingly the umpire used a ruler to move the pieces across the map. The game used dice to determine combat results and inflicted casualties, and the casualties inflicted by firearms and artillery decreased over distance. Unlike chess pieces, units in Reisswitz's game could suffer partial losses before being defeated, which were tracked on a sheet of paper (recreational gamers might call this "hitpoint tracking"). The game also had some rules that modeled morale and exhaustion.
Reisswitz's game also used an umpire. The players did not directly control the pieces on the game map. Rather, they wrote orders for their virtual troops on pieces of paper, which they submitted to the umpire. The umpire then moved the pieces across the game map according to how he judged the virtual troops would interpret and carry out their orders. When the troops engaged the enemy on the map, the umpire rolled the dice, computed the effects, and removed defeated units the from map. The umpire also managed secret information so as to simulate the fog of war. The umpire placed pieces on the map only for those units which he judged both sides could see. He kept a mental track of where the hidden units were, and only placed their pieces on the map when he judged they came into view of the enemy.
Earlier wargames had fixed victory conditions, such as occupying the enemy's fortress. By contrast, Reisswitz's wargame was open-ended. The umpire decided what the victory conditions were, if there were to be any, and they typically resembled the goals an actual army in battle might aim for. The emphasis was on the experience of decision-making and strategic thinking, not on competition. As Reisswitz himself wrote: "The winning or losing, in the sense of a card or board game, does not come into it."
In the English-speaking world, Reisswitz's wargame and its variants are called Kriegsspiel, which is the German word for "wargame".
The Prussian king and the General Staff officially endorsed Reisswitz's wargame, and by the end of the decade every German regiment had bought materials for it. This was thus the first wargame to be widely adopted by a military as a serious tool for training and research. Over the years, the Prussians developed new variations of Reisswitz's system to incorporate new technologies and doctrine.

Worldwide spread: Prussian wargaming attracted little attention outside Prussia until 1870, when Prussia defeated France in the Franco-Prussian War. Many credited Prussia's victory to its wargaming tradition. The Prussian army did not have any significant advantage in weaponry, numbers, or troop training, but it was the only army in the world that practiced wargaming. Civilians and military forces around the world now took a keen interest in the German military wargames, which foreigners referred to as Kriegsspiel (the German word for "wargame"). The first Kriegsspiel manual in English, based on the system of Wilhelm von Tschischwitz, was published in 1872 for the British army and received a royal endorsement. The world's first recreational wargaming club was the University Kriegspiel [sic] Club, founded in 1873 at Oxford University in England. In the United States, Charles Adiel Lewis Totten published Strategos, the American War Game in 1880, and William R. Livermore published The American Kriegsspiel in 1882, both heavily inspired by Prussian wargames. In 1894, the US Naval War College made wargaming a regular tool of instruction.

Miniature wargaming: The English writer H. G. Wells developed codified rules for playing with toy soldiers, which he published in a book titled Little Wars (1913). This is widely remembered as the first rulebook for miniature wargaming (for terrestrial armies, at least). Little Wars had very simple rules to make it fun and accessible to anyone. Little Wars did not use dice or computation to resolve fights. For artillery attacks, players used spring-loaded toy cannons which fired little wooden cylinders to physically knock over enemy models. As for infantry and cavalry, they could only engage in hand-to-hand combat (even if the figurines exhibited firearms). When two infantry units fought in close quarters, the units would suffer non-random losses determined by their relative sizes. Little Wars was designed for a large field of play, such as a lawn or the floor of a large room. An infantryman could move up to one foot per turn, and a cavalryman could move up to two feet per turn. To measure these distances, players used a two-foot long piece of string. Wells was also the first wargamer to use scale models of buildings, trees, and other terrain features to create a three-dimensional battlefield.
Wells' rulebook, however, failed to invigorate the miniature wargaming community. A possible reason was the two World Wars, which de-glamorized war and caused shortages of tin and lead that made model soldiers expensive. Another reason may have been the lack of magazines or clubs dedicated to miniature wargames. Miniature wargaming was seen as a niche within the larger hobby of making and collecting model soldiers.
In 1955, a California man named Jack Scruby began making inexpensive miniature models for miniature wargames out of type metal. Scruby's major contribution to the miniature wargaming hobby was to network players across America. At the time, the miniature wargaming community was minuscule, and players struggled to find each other. In 1956, Scruby organized the first miniature wargaming convention in America, which was attended by just fourteen people. From 1957 to 1962, he self-published the world's first wargaming magazine, titled The War Game Digest, through which wargamers could publish their rules and share game reports. It had less than two hundred subscribers, but it did establish a steadily growing community.
Around the same time in the United Kingdom, Donald Featherstone began writing an influential series of books on wargaming, which represented the first mainstream published contribution to wargaming since Little Wars. Titles included : War Games (1962), Advanced Wargames, Solo Wargaming, Wargame Campaigns, Battles with Model Tanks, Skirmish Wargaming. Such was the popularity of such titles that other authors were able to have published wargaming titles.