The 4X video game genre is a subgenre of the strategy genre. The name comes from the 4 "X"'s that comprise a summary of the genre's gameplay:
- X-Plore: Look around and find interesting things.
- X-Pand: Build more cities/colonies/space stations on the territory you just found.
- X-Ploit: Improve the cities/colonies/space stations through various means, making the most of the resources you have acquired.
- X-Terminate: Use those resources to kill everyone who isn't you and take their stuff.
In 4X games, you control an empire that is in competition with other empires. These "empires" can represent different clans, tribes or cultures, or even different alien races. Different empires may also have different advantages or disadvantages; some games even allow you to create customized empires on your own.
The empires will be competing over a region that could be as small as England, or as large as the Galaxy. Most members of the genre do not require that you play them on a specific piece of terrain. Instead, most of them offer a randomized map generator, typically with settings that affect the outcome (how many planets, how much water vs. land on Earth-like worlds, etc). The map almost always features some degree of Fog of War, requiring the player to devote resources to explore the map in order to discover new resources to exploit.
On whatever map the player chooses, there are territories on which you can build "cities" (whether planetary colonies, space stations, or just cities). Cities exploit the resources in the region where they are built, and can transform those resources into "buildings" (improvements to the city's efficiency), money, or units.
Units can move various distances on the map, possibly with terrain restrictions, and perform a variety of tasks — which may or may not include combat. You almost always have to produce a special type of unit that can create another city to let you expand your empire. Some games allow you to create customized units based on your technology base (see below), in addition to the default units included in the game.
Other empires work under the same restrictions as you (except when they are cheating bastards). You can talk to other empires, broker peace with them, trade with them, ally with them against a common foe, or kill them. Mostly kill them. Be careful: they will do the same to you, and they will remember what you've done to them.
Most 4X games feature a Tech Tree, though others may use Technology Levels instead; some even combine the two. Cities produce research, which is used to research new technologies. The Tech Tree is so named because you cannot research a technology until you have its prerequisites. You can't learn "Alphabet" until you've learned "Writing", for example. Technologies provide upgrades for cities, letting you better use their resources, build new units, buildings, or weapons, and so forth.
A staple of the genre, borrowed from the originator of the genre Civilization, is the "Wonder". It is a city-produced construct that only one city in the entire gameworld can produce. Whichever empire builds it first gets its benefits, and everyone else gets zilch. It generally confers a substantial benefit to the civilization that produced it, and it can only change hands if the city it is built in changes hands. More recent 4X games offer less powerful non-global "Wonders" that each empire can build, but can only be built in one of their cities. These typically provide a large bonus to a specific city.
One other staple originated by Civilization is the "goodie hut"; random local tribes/lost cargo pods/space anomalies that act as Inexplicable Treasure Chests for the first player to discover them. Of course, some of them can act as Chest Monsters, as well...
Just to make sure you can't be completely pacifist, you will usually encounter barbarian tribes (pirates/guerrillas/terrorists/angry alien fungi) that appear out of nowhere and cannot be negotiated with (although their units may be captured instead of destroyed if the player is clever).
Victory in 4X games will always be available by exterminating all or most of your opposition. However, 4X games are usually expected to offer one or more alternative victory conditions. Some allow you to pool your civilization's production in order to produce a gigantic monument, such as Civilization's UN Unity Spaceship, or Alpha Centauri's Ascent to Transcendence. If you can do that, spending all of those resources while defending your borders from people trying to stop you, you win. In some games, researching a long series of technologies (typically that do not provide any immediate benefit) causes victory. If you ally with all other (surviving) empires, then you win in some games. While all victory conditions are usually open to all players, some factions are often more suited to pursuing certain endgames than others.
Historical versions of the genre tend towards allowing Anachronism Stew, but at the direction of the player. A player's civilization might reach tanks and battleships by 1000 AD while the computer players are still in the iron age or develop genetic engineering before electricity. Futuristic versions tend to use a lot of Techno Babble in their unit/weapon/technology names and descriptions.
- As noted below, Avalon Hill's Civilization served as an inspiration for Sid Meier's video game of the same name.
- Fantasy Flight Games brought out a board game version of Sid Meier's Civilization in 2010, designed by Kevin Wilson. The game remains mostly faithful to its PC counterpart, with production, research, combat, multiple victory conditions and a hidden map to explore, while condensing the whole experience to around 4 hours.
- Twilight Imperium is basically Master of Orion as a boardgame.
- Eclipse is a similar space based 4X game, which has the, highly relative, distinction as a simplified, faster version of games like Twilight Imperium.
- Empires of the Void is another Space 4X boardgame, though as one reviewer points out, it lacks the eXploration component because the entire map is visible from the beginning of the game.
- Age of Empires is a Real-Time Strategy variation.
- Age of Wonders, a Spiritual Successor to Master of Magic.
- Anno Domini
- Armada 2526
- Ascendancy was a game that let you control your species from the individual planet-level project to managing the entire empire of star systems. It featured no less than twenty-one species, each with a different special ability - and humans aren't one of them.
- Aurora (4X) is a freeware 4X space game, and is considered the Dwarf Fortress of 4X games. it is notable for its expansiveness and unintuitive user interface (like Dwarf Fortress) and may be one of the most complicated space 4X games ever created. The game is more like a series of spreadsheets and drop-down lists than an actual game. Planets are generated with tectonics and ecosystems, ships must be carefully crafted with much thought put into the targeting and guidance systems as well as a whole plethora of minute details, armies and civilizations can be determined down to the individual person, needless to say this game is VERY detailed. It's available here.
- Battle of Polytopia
- Castles Siege And Conquest is a simple, somewhat realtime 4X game in which you compete with other lords for rulership of France using guile and diplomacy after the king dies without issue. Once you claim the throne, expect even your closest allies to immediately turn on you.
- The Civilization series invented, refined or codified most of the tropes of this genre. It allows the player to shepherd a civilization through Earth's history. It was originally based on a board game by Avalon Hill that allowed you to play from the Stone Age to the Roman Empire era.
- Colonization is Civilization in America! Though it has some significant differences: no tech tree, and most units are very, very specialized. Also, Wonders are replaced by "Founding Fathers" (plus Pocahontas.)
- Civilization: Call to Power is a nominal-only Civilization game/spin-off which features similar gameplay to Civilization II along with its own unique gameplay features. It also had units which didn't appear in the Civilization series proper, such as lawyers and mecha, until much later.
- Civilization: Beyond Earth, spin-off of Civilization V and Spiritual Successor to Sid Meiers Alpha Centauri.
- Cossacks, another Real-Time Strategy version.
- Deadlock and its successor Deadlock II had different races fighting over a series of planets within a "Dark Cloud". The original game had only one planet; in the sequel, the races discovered that there was actually a series of planets further in, all formerly owned by a mysterious ancient race. The plot revolved around finding the technologies and temples left behind by this ancient race.
- Distant Worlds
- Elemental - War of Magic, a Spiritual Successor to Master of Magic.
- Empire (a.k.a. Classic Empire)
- Endless Legend
- Endless Space
- The five Dominions games revolves around various entities attempting to achieve godhood through the expedient method of wiping out all competition. 4 adds the option to win by claiming and holding certain important locations instead, at which point you ascend and presumably destroy all competition afterwards.
- Empire Earth 2 combines many 4X elements with Real-Time Strategy using Tech Trees and civilization-specific wonders.
- Europa Universalis
- Freeciv is a very customizable Civilization clone.
- Galactic Civilizations and its sequel, GalCiv 2.
- Gihren's Greed is a 4X game based on Gundam, specifically the Universal Century continuity.
- Haegemonia: Legions of Iron: Spiritual Successor to Imperium Galactica II and borrows heavily from Master of Orion and Homeworld.
- Imperialism might be called a "3.5X": the entire map is visible at the start, but the player must build specialized units to see if there is gold in them thar hills. (Or iron, or coal, or diamonds.)
- Imperator: Rome
- Imperium Galactica and its sequel.
- King of Dragon Pass is a strange example including lots of RPG and Visual Novel elements.
- Leylines, an indie title involving wizards and world-destructive magic.
- Light of Altair, a welcoming, simplified indie title.
- Master of Magic, a fantasy-themed spinoff of Master of Orion, below.
- The term "4X" was coined in a review of the first installment of the Master of Orion series. Master of Orion 3 riffed off this by including "The X's" as actual MacGuffins within the game, including a semi-mythical "5th X".
- Neptune's Pride and its sequel, Triton, are browser-based free-to-play 4X games. They're played in real time, but very slowly, with travel times between stars measured in hours and resources paid out once per day. A typical game lasts from a few weeks to a month or more.
- Reach For The Stars
- Pandora: First Contact is a 4x game, made as a spiritual successor to Sid Meiers Alpha Centauri
- The Railroad Tycoon series, also started by Sid Meier, can broadly be characterized as one of these, with some subversions. Exploration is there, after a fashion, since maps are mostly randomized, although there is no Fog of War in effect. Expansion and exploitation are part-and-parcel of the game, and "extermination" takes the form of "bring every rival company on the map to ruin or bankruptcy".
- Rise of Nations, created when its developers realized they wanted a Real Time Civilization game.* It's an RTS with a "Risk"-Style Map, but covers a lot of the same ground.
- Shores of Hazeron is a MMO 4X played from the first person perspective.
- Sid Meiers Alpha Centauri is the spiritual "sequel" to Civilization IN SPACE!. The game's tagline is "Explore. Discover. Build. Conquer." They even managed to integrate that into the gameplay on a second level: Technologies are divided into types (Explore=scout/exploration/environmental technologies, Discover=pure science, Build=industrial technologies, Conquer=military tech) and a player can have the AI "Governor" of any given base focus on one or more tracks if he/she doesn't care for micromanaging.
- This game is also a bit rare among 4Xs for having a general plot. Through quotes when you construct structures, research technologies, and complete projects (Wonders), a loosely connected story is told, and a canon game progression is hinted at.
- Sid Meier's Starships is a turn-based strategy with the player controlling a fleet of ships exploring space.
- Sins of a Solar Empire is a spacegoing Real-Time Strategy game with shades of 4X.
- Spaceward Ho! is an interstellar 4X game with a Western theme.
- Space Empires, a series of highly-customizable 4X games with such an extensive system of micromanagement as to make the micromanagement need in the Civ games pale in comparison.
- Space Tyrant is Galactic Civilizations by way of Evil Genius; there is no diplomacy option, just meet interesting cultures and either exploit or exterminate them. As the name suggests, the Emperor of your civ is a Card-Carrying Villain trying to conquor the galaxy.
- Spore plays like one of these during the Tribal and Civilization Stages of the game.
- Starbase Orion started off as an iOS port for Master of Orion but has evolved since then.
- Star*Drive is a realtime example.
- Star Ruler is another Real-Time Strategy take.
- Star Ruler 2 refines the 4X mechanics of the first game.
- Stars Beyond Reach is half a hex-based 4X and half city builder.
- Stars! is a turn-based 4X space game released in 1995 for Windows 3.11 that continues to have a strong following online.
- Sword of the Stars: Turn-based on the strategic level, real-time on the tactical level. The intro even mentions two of the "x"s by name (and uses "conquer" instead of the last).
- The Tone Rebellion, a unique Real-Time Strategy with 4X elements.
- VGA Planets
- Victoria: An Empire Under the Sun
- Warhammer 40000 Gladius
- Warlock: Master Of The Arcane
- The X-Universe series is a real time space simulation like Elite that revolves around Mega-Corp management. The series' motto: "Trade. Fight. Build. Think."
- X-COM: UFO Defense combines 4X base-building and Real-Time with Pause interception missions with turn-based tactical battles. Terror from the Deep and Apocalypse follow in this trend (though Apocalypse modifies it significantly); Interceptor, Enforcer and the 2K Marin game The Bureau: XCOM Declassified abandon this. XCOM: Enemy Unknown and XCOM2 return to the tradition.
- The board/computer game Empire that is the source of the Wopuld family's wealth in Iain Banks' The Steep Approach to Garbadale is a particularly complicated one of these. A similar game, Despot, features in his earlier novel Complicity. The author is a confirmed fan of the genre; he's gone on record saying Civilization is one of his favorite games of all time.
- The Solar Empires series of video games in Austin Grossman's You are 4X games (among other things.) The term itself is dropped in the text.