The first multi-computer online game, Modem Wars was played over a modem connection between two machines (via telephone or null modem serial connection), with both players controlling a group of robotic units trying to eliminate the opponent's command center. Features such as fog of war, varied unit types, terrain, and formations, all now standards in the genre, were implemented despite the daunting technical limitations of late 1980s computers. As for the game's influence on other games, Scott Sharkey states that Modem Wars was perhaps "[t]he closest predecessor" to the groundbreaking and influential Sega Genesis real-time strategy game Herzog Zwei.
Of specific technical interest, Modem Wars has been lauded for its mechanism of using 4-byte packets for each 'move', deltas to determine game states, and storage of those deltas to allow for after-game replays.
The game was originally developed under the title "Sport of War"; Computer Gaming World noted this was the easiest way to understand the game, saying "You play the game as a wargame, but you accumulate points as if it were a sports game." The name was changed to Modem Wars to call attention to how the game is intended to be played against other humans via modem. The computer AI opponent is referred to as a "solo trainer", and CGW recommended against buying the game for those planning to only play against the computer.
The game also has a replay feature, referred to as a "game film". A separate utility allows replays to be uploaded to bulletin board systems for sharing.
In Computer Gaming World's review, Daniel Hockman noted designer Dan Bunten's intentions for the game:
"Dan would like us to believe that Modem Wars is "a wargame for the rest of us". That is, Modem Wars is a fast moving game that does not get bogged down in the minutiae of detail so often associated with wargames. Dan feels that Modem Wars is for those gamers who want to "play war" but are turned off by the detailed rules of the typical wargame."
Each player is presented with a map of which they control the lower half. Across the center is a line, below which they can set up their units. Each unit which crosses this line gains a point. If the ComCen crosses it, many additional points are scored. A second line is three quarters of the way up the screen; crossing it with units gives additional points. Crossing it with the ComCen is one way to win the game.
The map is made up of multiple types of terrain. Most of the space is clear, but there are also woods, which slow movement and reduce visibility, and hills, which slow movement and allow units atop them to have a small range and damage bonus, while those climbing have a small damage penalty.
Optionally, a Recycler space can be made available, which will regenerate destroyed units. A recycled unit must be moved off the Recycler for another unit to appear, and it can be blocked by enemy units. There are three options: None, Half, and Full; Half will recycle only half the units you've lost.
The bulk of the player's army consists of Grunts, which have respectable capabilities. There is a modest contingent of Riders, which are faster than Grunts, but which have less firepower and armor. (In total, there are just enough Grunts and Riders to stretch all the way across the width of the screen.) Next is a small contingent of Boomers, which are artillery pieces. They have longer range and do significant damage to other units except other Boomers. Each of the three Spies is a fast, rugged unit with extended range sensors, but no weapons, which are useful for finding enemy units, especially the ComCen. Spies are also very useful for blocking the enemy Recycler, if present. And lastly is the Command Center, aka the Quarterback, aka the ComCen. The ComCen is the player's seat in the battle. It has a limited number of missiles for self-defense, heavy armor, and a radar screen which is capable of spotting enemy spies. If it uses its missiles, it becomes visible on the main map and enemy radar screen for several seconds. Destroying the enemy ComCen is another way to win.
Units can be collected into groups for easier management.
Units also have two special modes of operation. First is Digging In. A dug-in unit deals additional damage at longer range and takes less damage from enemy fire, but can't move. It takes a few seconds to dig in or out, though units can start the game dug in. The second mode is Shadow mode, which reduces the distance at which other units can see it; however, while in this mode, it cannot see or shoot. The ComCen cannot use either of these modes.
There are three ways to win the game: getting the player's ComCen across the opposing goal line, 3/4 of the way across the screen; knocking out the enemy ComCen; and having the highest score when time runs out.
Points are scored by sending units across the middle and the goal lines.
In a 1992 survey of science fiction games, Computer Gaming World gave the title three of five stars.