Sid Meier's Alpha Centauri/Gameplay

The precise goals of the game vary from game to game, although all games employ conquest (eliminating all other players) and histographic (have the highest score after a set number of turns) methods of victory. In many games, more are employed, such as the "space race" (construct a spaceship that consists of multiple parts), "domination" (have most of the map within the reach of your cities), "regicide" (kill a specific unit), or "transcendence" (the researching of a specific technology).

As in chess, the game is divided into several phases and the ultimate goal of the game should not distract you from playing each phase correctly. Checking the king without purpose is useless in chess, as is making empty threats for no reason other than to make threats in Civ. In both games, an empty threat may or may not be effective, but for it to be truly effective it must have sound reasoning behind it, and if it does not work it must not punish the player who made the threat.

Cities
All Civilization games have cities. Alpha Centauri refers to them as "bases", Colonization as "colonies", but they serve exactly the same function.

The primary function of a city is production: food, military or other units, and/or structures (including facilities for increasing defensive strength of the units in the city).

The secondary function of a city is acquiring and holding territory. By acquiring territory, you reduce your enemy's possibilities for production and/or efficient movement. Therefore, an unproductive city can be useful even if "loss-making", but a productive city will almost always be more useful.

The ideal city serves both functions.

Good city sites
The details of what constitutes a good city site depend on the game. For instance, in Alpha Centauri, high elevation is desirable. However, most other Civilization games have no concept of elevation. What they do share in common is that different terrain will produce different resources and have different defensive capabilities. Therefore, what makes a certain site desirable is always the same: an abundance of resources and an ability for the city to defend itself.

On worldwide considerations, proximity to your other cities is advantageous too. The different games have different ways of making that count.

Resources and production
Cities (except in Colonization) always produce three resources. These are usually named food, shields, and trade. In SMAC, these are called nutrients, minerals, and energy, respectively. In Civilization III, "trade" was renamed "commerce". In Civilization II: Test of Time, the names depend on the current game being played. Regardless of their names, they always serve the same functions. For consistency, we will refer to them as food, shields, and trade.

All games have cities, each populated by at least one "citizen" (which term here includes people such as slaves). They will work the surrounding terrain and produce goods. Each citizen may work one tile; the central city tile is always worked automatically when the city is created. For instance, a city with 6 citizens can work up to seven tiles: the center tile plus one tile per citizen. In most Civ games, citizens are restricted to the tiles they can work to a city radius. However, any one tile on the map may only be worked by a single laborer within a single city: that is, if two cities have overlapping city radii, a laborer working a tile within the overlap within one city will prevent laborers from any other city from working the same tile location in the second city. Citizens can also be specialists and not work tiles; this will be discussed later. Civ cities contain 21 tiles (a 5 by 5 square without the corners), Colonization colonies contain 9 tiles.
 * Colonization allows citizens to do specific indoor work, in purpose-built or pre-existing buildings. Most of the high-value production comes from this work.

These are the three kinds of goods that your cities will produce:
 * Food - No civilization can survive without food. Surplus food will accumulate until the food box is full. When it is filled, another citizen will be added to the city and the food box will empty. The food box grows with the size of the city, (and thus requires ever more surplus food to fill it in order to get the next citizen or worker), usually at a constant rate. Each citizen requires two food per turn to survive. A citizen will never take more or less than this. If the city is not producing enough food to meet demand, this food will be taken from the food box. If the food box is empty and a citizen still must eat, a citizen starves and the population count will be reduced by one. In some Civ games, Settlers units need support in the form of food from their home city in addition to the shields they need for support. In these cases, if the food box empties and more food is needed, the most distant such unit will be disbanded. If more food is still needed after that, then a citizen will die. The population count will never be reduced by more than one per turn due to starvation.


 * In many Civ games, improvements and wonders may also affect how food is used to create new citizens. For example, many Civ games have the Granary (a city improvement) that only half-empties the food box upon creation of a new citizen, dramatically reducing the time required to refill it, and a wonder that gives Granaries to every friendly city.  In Civilization III, possession of the Longevity wonder will make your cities create two citizens instead of one when the food box fills.  In other cases, a new citizen may not be created when the food box is full because of the city reaching a population limit. (The food box may nevertheless lose all or half its store, with no compensation.)


 * Shields - A city must produce raw materials (shields), which can then be used to build things. (The Colonization equivalent is "hammers", produced from lumber.) Your city will always be working on one of three kinds of projects:
 * Unit - Build a unit, such as a military unit or Settler.
 * Improvement - An improvement to benefit the city, or a Wonder to benefit much or all of your entire civilization or even the entire world, but which is physically located in the city that built it (and passes to a rival, unless destroyed, if the city is captured).
 * Capitalization (in some games, Wealth) - Shields are converted to gold for the player's treasury, usually with a heavy penalty (e.g., four shields is converted to one trade unit). Civ 2 does not have this penalty. Completed buildings may be "sold" on a 1:1 basis in most games. In Civ IV, the ability to create research and culture'' was added.


 * Shields are added to the shield box (except that when "building" Capitalization the gold generated goes into the treasury instead). When the shield box is full, production is complete and the unit or improvement is immediately available. In most Civ games, but not the latest versions, III and IV, shields are also used to support units beyond those that are deemed "free". If more shields are needed by units than are being collected in the city, then in Civilization a unit is disbanded, but in other versions the needed shields are removed from the shield box. If the box empties but more shields are still needed, one unit will randomly be disbanded. In most games, shields in the shield box can be destroyed through espionage activities of the Spy unit.


 * Trade - Every civilization has some form of currency or barter system. You allocate the total trade resources of your civilization on the "set tax rate" screen (except that in Colonization the Monarch back in Europe sets the rate of excise duty on goods you sell there).
 * Each turn, the trade resource is "spent" according to the rates you set on at least one of three things:


 * Tax - The trade goods become money in your civilization treasury. You can use it to rush-build, given the right conditions, use it as part of a trade with another civilization, or even give it as a gift. Tax revenue is also used to pay required maintenance fees for improvements and wonders, as well as, in the latest versions, support and upgrade your units.
 * Science - The trade goods go toward scientific research, allowing you to research new technologies that can unlock new units, improvements, wonders, and unit abilities. Falling too far behind your competitors in the science race the most reliable way to lose the game. (As mentioned below, the Colonization equivalent is the Liberty Bell, where the "new technologies", such as faster ships or greater production, are called "Founding Fathers".)
 * Luxury/Culture - The trade goods go toward entertaining the populace, keeping them happy or content, which increasingly becomes a factor the larger your city population becomes. In addition, in some games, the more cities you have, the sooner you have to deal with unhappy citizens.  In many Civ games, luxury output first transforms content citizens to happy ones, then, if there are still unallocated luxury output and no content citizens, transforms unhappy citizens to content, then happy, citizens.  Angry citizens and resisters are generally unaffected by luxuries. This was replaced in Civilization IV by a culture slider, accessible  with music. Commerce is diverted to producing culture, which expands you boarders and, with some buildings, helps to make citizens happy.

Colonization
Colonization, instead, has 16 types of "cargo" produced, some "gathered" directly from the terrain and some produced by conversion of another (or, in the case of horses, just fed with surplus food production as long as there are two or more). They can all be bought or sold for money and moved in ships or wagon trains. Two other elements can be produced but not traded.
 * Food, one of the 16 cargoes, is needed to sustain workers (two units each per turn as in the other Civ games), and is exchanged for a new colonist in a colony that has a 200-ton surplus after the end of a turn. Colonists who are not working in a colony (eg traveling (with or without horses or engineering tools) or engaged in defence duties) need no food or other support.
 * Forests can be worked for lumber, tradeable as one of the 16 cargos but having prime value when converted by carpenters into hammers (the equivalent of Civ shields) for producing units, ships, wagon trains, and structures.
 * The Colonization equivalent of "science" is the Liberty Bell (produced to a limited degree by every colony but much more where a worker works in the Town Hall and still more if he's an Elder Statesman), which (in addition to an effect on the productivity of the colony that produced it) goes toward having successive "Founding Fathers" joining your Continental Congress and thereafter providing your empire with various benefits, some major and some minor.
 * An extra feature of production is the cross, produced to a limited degree by every colony but much more where a church is built and staffed and still more where a Firebrand Preacher is installed: crosses go towards encouraging fare-paying emigrants from the religious persecution of Europe attracted to your religious freedom.

Corruption and waste
Resource output can be lost through corruption, although in many games there is no corruption of food. Corruption of shields is generally known as waste. In many games, the amount of corruption is heavily dependent on the distance a city is from the civilization's capital city, as well as the overall number of cities controlled by a civilization. Some games may also have an upper limit on the amount of corruption a city can have, so that a city that suffers heavy corruption could still be productive. The amount of corruption also depends on the presence of certain improvements that reduce corruption, the type of government, as well as whether a city is celebrating "We Love the King Day".

In Civilization IV, this concep is replaced with maintenance, which goes up exponentially with the number of cities you rule and their distance from your palace.

Many games have a civilization starting in a form of government with relatively high corruption, with scientific achievement allowing switching to a form of government with less corruption. In many games, there is also a form of government in which the distance factor is eliminated, while other forms of government eliminate corruption altogether. When switching between governments, it is typical that neither shields nor trade are produced, or conversely, cities in a state of anarchy suffer total shield and trade corruption.

In many Civilization games, the Courthouse city improvement (available with the Code of laws technology) reduces a city's corruption and waste substantially.

Citizen happiness
For your cities to be productive, their citizens must be kept content. There are generally four degrees of happiness in a Civ game. From most happy to least happy, they are:
 * Happy
 * Content (normal)
 * Unhappy
 * Angry

Unhappy citizens are created from numerous sources. One of the most common is unhappiness due to overpopulation, in which new citizens from city growth are created unhappy. This is generally dependent on the difficulty setting in a game, with the highest difficulty level having its second and subsequent citizens in a city born unhappy. Other sources of unhappiness in many Civ games include having military units away from home, drafting citizens, or war weariness.

If the number of unhappy people exceeds the number of happy people in a city, the city will fall into civil disorder. Content citizens and specialists do not enter the equation. When a city is in civil disorder, no goods are produced other than food. In some games, you cannot rush-build during disorder as well. In many games, there are city improvements that are dangerous to have in a city under civil disorder, such as nuclear power plants and their risks of meltdown. Prolonged civil disorder in a city, or multiple cities under civil order, may lead the citizens to destroying certain city improvements (but never wonders), or, in the worst case, revolt, sending your government to anarchy. This is especially true of representative governments such as Democracy in many Civ games, where having two cities in civil disorder, or one city for more than one turn, will lead to a revolution.

This, however, is not true of Civilization IV. Instead, 'happiness' and 'unhappiness' modifiers are listed. For each point the unhappiness modifiers exceed the happiness ones, one citizen will refuse to work. Cities never revolt.

A city may also turn some or all of its citizens into specialists. In some games, this ability is restricted to cities above a certain size. Specialists are always considered content, and do not work a tile in the city radius, but instead produce other effects. Many Civ games have at least three kinds of specialists: taxmen, who create additional gold for a player's treasury; scientists, who contribute to research; and entertainers, who create luxuries that can content unhappy citizens or turn content citizens happy.

Civilization IV uses a whole new system of specialists, with more impressive attributes and greater variety.

Angry citizens usually appear only after capturing an enemy city, being loyal to their mother country. Angry citizens refuse to work for the new regime, and thus do not contribute anything to the city, and cannot be converted to a specialist, and in some games, rush-building is impossible while an angry citizen exists. Many strategies of dealing with angry citizens include starvation and the garrisoning of strong defensive troops. Sid Meier's Alpha Centauri does not have angry citizens, having Drones (unhappy citizens) serve both roles.

In many games, there is an additional incentive for having happy citizens, as, with the exception of angry citizens, there is no production bonus or penalty associated with the mood of a citizen and its association with the tile they work on. This incentive is called "We Love the King Day" (although in many cases "King" is substituted for a title based on the government, EG. in Communism it's "Comrade"). This occurs when there are no angry or unhappy citizens, there are more happy citizens than content citizens, and the city is growing. "We Love the King Day" generally brings reduced corruption and waste to a city, and may bring forth additional production through production bonuses or the elimination of production penalties, depending on the type of government. In some games, and under representative governments, a city may even spontaneously grow in size. In a histographic game, happy citizens contribute more to the score than content citizens.


 * Colonization has a similar productivity loss when the number of Loyalists in a colony exceeds a fixed number (which varies with the "Degree of Difficulty"). The solution is to increase production of Liberty Bells so as to increase the proportion of citizens who are of the Rebel persuasion instead.

Research
Each turn of the game, you have a chance to accumulate research toward a civilization advance, often simplified to "tech". Techs will grant you new capabilities, or at least the chance to acquire them later, and can be used as a trading item. The only circumstances you will not accumulate research are if you have no cities, your research rate is at 0% and you do not employ scientists, or you have cities and a research rate but are not generating sufficient trade in any cities to put taxes into research.

The technologies always follow a hierarchy, called the "tech tree". All but the most basic techs require knowledge of two others if you are to research them. Most Civ games have one huge tech tree, but certain games (and certain scenarios therein), such as Civilization III, have multiple tech trees. All the games have extremely different tech trees, but they all share similarities. For instance, many players could not tell you the exact effects of "Electricity" for every single Civ game without looking it up (but good players will certainly know them for their favorite games). This is because the name of the tech may have little to do with its effects.

Choosing which tech to start researching is an important decision. It matters even more in the early game, as each tech usually takes many turns to research (with the increased "cost" of each successive one offset by your greater productivity). Researching many techs early can trigger a game-lasting advantage. Whatever you do, make sure (except when at war sometimes) to keep researching down the path that your strategy is based on. You won't get very far in war against a much more advanced civilization.

From Civ2 onwards, there's on-screen help in deciding which tech to try next, but in Civ1 you rely on your memory or the manual.

If in contact with other civs or expecting to be, it is a good idea to research the most advanced tech available because it is most likely to be tradeable.

In some games the Great Library gives you any tech discovered by two or more other civs. If you have it, you can often profitably sell libraries and set science to a minimum and concentrate on tax and luxuries, until the Library ceases to be effective.

Expansion phase
The first phase of any Civ game is the expansion phase. Each civilization tries to stake its claim to as much territory as it can, possibly even knocking out a rival with a "rush". The details of this will differ from game to game and from player to player. For instance, in Civilization I and II, a player might place cities as far apart as necessary to avoid overlap, four squares between cities, not including the cities themselves, being roughly optimal. In Civilization III, the same player might place cities extremely close together, with two squares between cities, or even one square in extreme situations. All games share a need to produce colonizing units as fast as practicable in the expansion phase.

However, following this strategy in Civilization IV will lead to rampant costs, and potentially damage your economy permanently. As such, player have come up with a '60% rule': expand until you are forced to lower your science to 60% to stay in the black.

Infinite City Sprawl
Infinite City Sprawl (ICS for short; "smallpox" in FreeCiv), refers to the strategy based on the concept that a player should have as many cities as possible to crank out hordes of cheap military units. In Civ1, this is marked by building many cities adjacent to other cities without so much as a space in between. This strategy was so powerful that in all other Civ games, it is illegal to place a city immediately next to another. So players started placing them with a one-square buffer zone in between. Civ2 did have some other countermeasures in place, such as having too many cities will cause unhappiness problems, but on the whole, using ICS was far more effective than not using it would be. Against a player already known to use ICS, the only real effective response was to also use ICS. Because this simplifies the game to an absurd degree and increases the tedium, many players hated ICS and players would usually forego their differences to gang up on anybody found to be using it. To this day, using ICS against human opponents in Civilization I or II is a serious breach of playing etiquette.

ICS as an "unbeatable" strategy came to an end by Alpha Centauri or Civilization III, although it can still be an effective strategy and many players will still use it, while facing much less hostility in response because the strategy is now beatable by other means.

Diplomacy and the meta-game
The term "meta-game" when applied to Civ diplomacy was possibly first proposed by Velociryx, one of the acknowledged masters of Civilization-style games. It is difficult to define this concept precisely, but it refers to idea that diplomacy is a game in itself, with its own rules and strategies, particularly in the way that three civs can interact with one another.

Warfare
No matter what you do, it's likely you'll eventually end up in a state of war with someone. Sometimes the warring parties are too far apart to actually engage in combat, and declaring war is mostly a token way of saying "I hate you". (Don't rely on that, though: sometimes they'll send in the navy or air force!) In the original Civilization all computer players tended to become aggressive and warlike after extensive contact, it can be an effective strategy to be more aggressive than your enemies through constant conquest of their cities.

Combat mechanics
In every game there is a way of fighting against either barbarians or other players. What determines the outcome of the battle is largely the same in every game. Each unit in any Civ(except Civilization IV, where it is represented by 'strength' and 'movement', accompanied by a large selection of modifiers and promotions) game has an attack/defense/movement rating (or ADM rating), which determines its power when attacking other units, its power in resisting attacks, and how many spaces it can move (or, if attacking, how many attacks it can make in one turn). The ADM rating can be modified by various factors, such as "veteran status", the terrain it is in, and whether the unit is in a fortified position.

In each turn of Civ, every unit has a chance to move to an adjacent square. Each type of terrain has its own movement cost, and the movement cost is taken out of a unit's movement rating whenever it moves. The movement ends for a unit whenever a unit's movement rating falls below zero for the turn. Movement points are replenished every turn. Most games also have a form of terrain enhancement that would reduce or eliminate movement costs for units. In some games, some forms of terrain are impassible. Also, some games may also have air units that use a fuel system, and thus must return to a form of refueling station (such as a city or airbase) after a certain number of turns. In addition to ADM ratings, many Civ games also have a hit point system, where a unit is destroyed when out of hit points (instead of instantly, as in the early games).

Many games allow the possibility for a unit to have a fractional amount of movement points, due to terrain features or terrain improvements that allow a unit to only expend a fractional amount of movement points to move to the tile. In some games, exhaustion also comes into play: if there is an insufficient amount of movement points remaining, a unit may not move to a tile as commanded, and if a unit is ordered to attack, its attack strength may be reduced. Injury has a similar effect in games that have hit points. In Colonization, sailing close to an enemy ship may reduce movement points, which can be serious if "you" were expecting to slip into a safe port.

Zones of control
In many games, units exert a zone of control. With the notable exception of Civilization III, whose definition of "zone of control" is considerably different, a unit's zone of control is the eight tiles that surround the tile which the unit is on. It is generally illegal for a unit that is in an opposing civilization's zone of control to move into a space that is in another opposing zone of control. This not need be the same unit, or the same player. Thus, it is sometimes possible to form a defensive barrier using units that are strategically placed.

Units of an allied civilization, or similar "right of passage" agreement, ignore zones of control. Some units can also ignore zones of control, regardless of their nationality.

Combat experience
Many Civ games also employ a system of combat experience. A regular unit may be promoted to Veteran status, and receive certain statistic bonuses. Veteran units in some games may be promoted further for more bonuses.

Nuclear warfare
All Civ games except Colonization allow the possibility of nuclear war. For instance, all Civ games have nuclear warheads, and Civilization II allows spies to detonate nuclear devices. (The retrovirus Probe Team action in Sid Meier's Alpha Centauri is similar to this.) Use of a nuclear weapon usually has the following effects:
 * If aimed at a city, half of its population dies
 * If aimed at a stack of military units, the stack is completely destroyed. In Civilization III, however, there is a 50% chance that a unit in a stack survives with 50% health.
 * Surrounding tiles have pollution added, influencing the possibility of global warming. In Civilization III, any terrain improvements on these tiles are also destroyed.
 * In many games, every civilization will declare war on anyone that uses a nuclear weapon. In Sid Meier's Alpha Centauri, this happens only if the UN charter is in effect.  In any case, the reputation of the user of the nuclear weapon is greatly soured.

Using nuclear weapons is not recommended unless you either have a lock on the game and want to finish it more quickly, or are in such a desperate losing position that it is the only thing that may turn the tide in your favor. Of course, if you are playing a one-on-one game, or all civs but you and another civ are eliminated, and you are at war with the other civ, you shouldn't worry about other civs declaring war on you, because there is no other civ to declare war on you!