Lyle Rains's and Ed Logg's Asteroids offered a terrific innovation that fundamentally altered Spacewar!'s gameplay concepts. Instead of blasting a rival space pilot, Asteroids had players destroying huge asteroids. Every time an asteroid was hit, it splintered into pieces, any one of which would destroy the player's ship in a collision. As with Spacewar!, players could hit a button to zoom into hyperspace, but might reappear in an even more dangerous situation than before. Asteroids was a huge success for Atari, and has been ported, cloned, and modified ever since.

Screenshot for XYPE's 2003 release of Thrust+ PlatinumThrust+ for the Atari 2600 Video Computer System. Platinum featured both gravity effects and momentum as critical components of its gameplay. 

Despite the success of Asteroids and Space Wars, enthusiasm for this style of game seemed to ebb soon after the introduction of Taito's Space Invaders in 1978 (see book Chapter 16, "Space Invaders (1978): The Japanese Descend").

Space Invaders gobbled up far more quarters than any of the old gravity-and-thrust games, which suggested that realistic physics wasn't all that important to most gamers.

Soon enough, games that required players to deal with complex issues of inertia and momentum were pushed to the dustier corners of the arcade.

A simulated view of a worse-for-the-wear Asteroids arcade machine.

Then again, we might see Spacewar!'s influence on other types of games that greatly benefited from accurate physics. This influence is perhaps most keenly felt in the simulation genres, particularly with flight simulators (book Chapter 8) and racing games (book Chapter 14, "Pole Position (1982): Where the Raster Meets the Road"). However, it's also the driving principle behind virtual pinball games (bonus chapter, "Pinball Construction Set: Launching Millions of Creative Possibilities").

Clearly, all of these types of games have relied heavily on complex "physics engines" to make their gameplay feel more like the real thing. We're also starting to see more and more discussion of physics in the first- and third-person shooter genres (book Chapter 5, "Doom (1993): The First-Person Shooter Takes Control").

It's no longer acceptable for such a game to show the same bloody mess every time the player shoots an enemy, for instance. If the enemy is hit at point-blank range with a shotgun, it ought to go flying back, perhaps bouncing off a wall or two before finally settling down to wallow in its puddle of blood.

Screenshot from Midway's Omega Race from 1981, with simulated color backdrop. Omega Race was an interesting mix of elements from Spacewar! and Asteroids in an enclosed environment.

Spacewar!'s ultimate contribution however, might be its depiction of a virtual world. Although some might argue that even a tic-tac-toe or tennis game features some sort of virtual world, we don't necessarily agree.

We should understand the difference between a game surface, such as a tennis court or chessboard, and a game world, such as the outer space environment of Spacewar! or one of the islands of Myst (book Chapter 12, "Myst (1993): Launching Multimedia Worlds").

Though we could easily get bogged down in theoretical discussions of "navigable space" and "habitable environments," suffice it to say that Spacewar! introduced gamers and developers to the notion that computers could represent and let players explore coherent virtual worlds, not just simulate simple motions in abstract space.

You didn't just play with these toys; you played in them. Though later games would of course dramatically refine the concept, it should be clear enough that even with Spacewar! we see lavish attention paid to defining the game world and making it feel realistic -- even going so far as to offer a realistic star map!

As the name so profoundly suggests, Spacewar! isn't about Xs and Os on a board, but a war in (navigable) space. For many computer scientists and engineers accustomed to seeing computers as nothing but expensive tabulating machines, it must have been a revelation to see Spacewar! for the first time. No doubt a few of them might have wondered, "What have we done?" while waiting impatiently for a turn. Steve "Slug" Russell had given us space.

[NOTE: For further reading, Gamasutra has also published a history of Spacewar! written by Game Developer magazine's Jeff Fleming, covering the game from a more first-person perspective, thanks to an interview with game co-creator J.M. “Shag” Graetz.]