Sid Meier's Alpha Centauri/Winning tips

These tips helps you to become world dominating power. After you reach this point you can do whatever you desire and don't need these tips anymore since you are practically won the game anyway.

Expansion
Like in many 4X games, your goal in the early expansion phase is to have lots of 1-population bases ("infinite city spam" / "smallpox") within 2 or 3 tiles of each other, connected by roads. This lets you adapt quickly to raids from wild Mind Worms or early aggressive neighbors, by quickly moving whatever defense units you have from one base to the next in a "bucket brigade", leaving central / distant bases without a defense unit and with the bases being raided with multiple defense units. Unless your Support setting is particularly low (which is unlikely until later in the game) each base can support one unit for free, so more bases means more freely-supported units, and the center tile of the base is always worked for free without requiring a population point, thus making smallpox the most optimal expansion doctrine.

Factions contacts

 * Make pact with other players if possible and exchange maps. This uncovers planet surface early on saving you on exploration and feeding your intelligence.
 * Pact factions gives you connection to other factions for free. This is a nice bonus. If you cannot make a pact with the faction buy connection to other factions anyway. It's cheap.
 * Pact factions also automatically share their map with you every time you contact them. So if you have pact with some faction, share all other faction contacts you have with them. Often they immediately exchange maps behind the scene. Close diplomacy dialog with you pact faction and open it again. They will offer you new map for price - refuse it. Maps will be shared automatically anyway for free.
 * Try not to share faction contacts with others if you are not a potential planetary governor nominee. Otherwise, if somebody gets all contacts they call election and somebody else will become a governor. Which is slight disadvantage for you.

Peace/War balance
Conquering enemy bases and territory with resources is good but spending your resources on building units is bad. Therefore, weight your options on how effective war would be for you at the moment. Successful war bumps your development whereas unsuccessful one throws you into abyss. Besides, conquering other factions is not always good thing. First, your empire stretches and bureaucracy increase impacts all of your cities including already well developed ones. Second, computer has development advantage. So it may be beneficial to evolve together with friendly factions thus boosting technology research and commerce to achieve transcendence victory quickly.

Maintain good relationships and integrity as long as possible
Other factions are pretty aggressive. They become even more aggressive as game progresses. They become even more aggressive when you break your promises (lower your integrity). They become even more aggressive if you become more powerful. That means when as you grow your power they all start harassing and attacking you. You'll be dead long before the time of your supremacy. Therefore, maintain good relationships with as most of them as possible for as long as possible through the course of the game. You will be definitely fighting somebody from time to time but better one at a time than all of them at once.

Gather intelligence and analyze neighbors
You need to know your opponents to make right decision.
 * Survey territory both land and sea and find out other faction placement and borders.
 * Infiltrate their datalinks, i.e. send a Probe Team to their base and select "Infiltrate Datalinks". That gives you HUGE intelligence!
 * Study their social choice, agenda and personality.

General peace/war decision points
The most important consideration here is that faction you attack will hold grudge and will try to retaliate whenever possible. They will never make pact with you again, will block your council proposals, and will gladly ally with your enemies. Weight your decision.
 * Research and review all factions around the globe periodically. Try to predict their next move based on existing alliances and mood change. Usually you'll get clear pointers that they are ready to have at you when they demand money/technology.
 * Prepare for future war(s). Do not let others to declare war to you on their terms. Get ready for the right moment and drive the events. Pacify angry factions until you are ready to confront them. Then it is easy to piss them off by constantly demanding to remove their forces from your borders.
 * Pay attention to the movements of military units of other factions. If they're moving near your territory they are probably planning to attack you soon, even if they are currently in Trade or Pact; be prepared to defend.
 * Compare your military strength. Start war only if you are either able to conquer their empire completely or scare them enough to make truce and block their potential future retaliation. Do not start the invasion if they are able to stop it and counterattack. This will be the end of your career as you'll get a mortal enemy for the rest of the game.
 * If your military strength is not yet enough to invade but the war is inevitable - prepare for defense. This is better from political point of view as you can get sympathy and help from other factions. Building impenetrable defense is cheaper. So you can continue to develop economically while draining enemy resources and preparing retaliation. See more detailed notes on defense tactics below.

Very early in the game
At the beginning you don't have much intelligence about your opponents to base your decision on. It is a matter of insight and judgement. Use below pointers.
 * One side has obvious military superiority.
 * They have Synthmetal Armor or better and you don't have Orge or worms. Make peace and pact by all means as they are unbeatable by you at the moment anyway.
 * You have Orge or worms in quantities enough to take at least two of their cities. Aid them with 1-2 scouts, concentrate your forces on their base and attack.
 * Otherwise.
 * They are pretty far away and do not immediately block your early expansion. Like their closes base is ~20 squares away or your have other direction to expand. Make a peace and pact if possible, exchange maps, save on exploration.
 * They are close and immediately block your early expansion. Like you have nowhere else to go or they are claiming the only useful landmark nearby. Don't make a peace, build as much scouts as you can support and send them to their direction. Find their cities and attack if they are indeed undesirably placed. Otherwise, you can make peace and send your scouts to exploration.

Later in the game

 * Conquer adjacent factions to expand. Try not to fight adjacent factions without explicit benefit, though.
 * Fight far factions with your ally hands to weaken both enemies and allies.

Defense tactics
Your best defense tactic is an active defense. Concentrate defending army in area where you expect massive number of enemy attackers. Your goal is to effectively wipe off attackers approaching your cities turn after turn eroding opponent's army but preserving and building up your own until such time when you are strong enough to launch counterinvasion or just keep them at bay forever. For that you need to have defensive facilities (perimeter defense, naval yard, aerospace complex) plus adequate number of garrison units protecting your cities. The goal of your garrison is stop or slow down fast enemy attackers and preserve your own fast attacker for retaliation. The best scenario is to let them come right to the city. This way your counterattacker don't need to leave the city at all while attacking. However, it is fine to get one square out of the city for counterattack if you can return your unit safely back next turn. This requires good coordination of building and mixing different unit types. However, once you achieved perfect mix, you'll get economical upper hand. Here is the checklist.
 * Select vulnerable cities depending on enemy units reach (land: borders, air: 10 squares from enemy bases, sea: all).
 * Build defensive facilities in vulnerable cities (land: Perimeter Defense, sea: Naval Yard, air: Aerospace Complex).
 * Put best armored defenders with suitable enhancements (land: ECM, air: AAA, worms: empath) in your vulnerable cities in numbers enough to stop or absorb two attack waves. Not that you want them to die but you want to have some cushion of protection for your counterattackers.
 * Put any number of fast attackers (the more the merrier) to actually knock out enemy units: rovers or needlejets if you have them. If opponent has air, add some number of anti-air units.
 * Important! Keep at least one probe team in each borderline base in case enemy probe team get lucky to the city.
 * For land only combats, clean terrain in front of the city. Do not leave any defensive terrain enemy unit can step on. Also remove all roads to slow them down.

Diplomacy
Make peace and pact with everybody you can at the beginning. This will allow you to easily control the situation later on. When AI fight other faction it tend to throw all resources to the war delaying own development and, most importantly, not starting secret projects leaving you more time to build them for yourself. So your strategy should be 1) to involve every faction into war and 2) direct their aggression to prevent unlimited growth of one AI faction. Here are few scenarios.
 * If you find the rather powerful faction that is weaker than combined power of other factions of its neighbors, make them fight with this strong faction together. Don't let them fight between each other. Even better if you can declare war to the common enemy too. This way they will grow to like you more and you'll secure pacts with them in time. Having pacts with all but one faction helps to support status quo longer and gain valuable time for your development.
 * However, if this powerful faction is not limited by its neighbors, don't let it fight them! Otherwise, it will just grow stronger by conquering them one by one. The better way would be to ally with such faction and declare war to some other out of reach faction. Faction on the other continent or Pirates are perfect choice. This way the development of your potentially strong faction will be impeded by war but it won't be able to conquer your mutual enemy. Thus their whole army potential will go to waste.

Economical growth
Should AI play as good as player in all areas it would be almost impossible to beat it on hardest level since it has 70% production bonus. It has one major flaw, though. Terraforming. Properly used condencers, boreholes, and mirrors boost your city parameters (growth, production, energy) 2-4 times comparing to undevelopped city. AI doesn't do it. So, as soon as you acquire technologies, build 2-3 formers per city and start terraforming like crazy. Your completely terraformed cities will produce technolgies twice as fast comparing to underdevelopped AI emprire of equal size. That is your game turning point. You need time of undisturbed development to get there, though. That's why you need to master war and diplomacy.

Terraforming hints

 * River is a pure bonus. No ecological damage too! Drill as much rivers as you can. The game is buggy and as long as a river does not yet exist, you can have multiple terraformers drill on adjacent tiles simultaneously.
 * Place mirrors and collectors in straight interlacing lines (line of mirrors, line of collectors, etc.). This gives you +3 energy per mirror/collector tile on average - best configuration possible.
 * For added bonus, if you can enclose a high-altitude area, instead of building bases there, you can build a solar farm: just do the interlacing lines and send Supply Crawlers from your science base (i.e. the one where you put all the research-boosting Secret Projects) to the solar farm. You can do something similar with an enclosed sea, creating tidal harnesses and sending Supply Crawlers from your science base there, though a solar farm can get you more raw energy per tile.
 * Forests are the best thing your Formers can do in the early game.
 * They convert every tile to a 1/2/1 tile. Early in the game, with the 2-resource limit, this is quite close to optimal.  An Arid/Flat (0/0/0), Arid/Rolling (0/1/0), or Moist/Flat (1/0/0) tile would be greatly improved by a Forest --- a Farm would only give +1 Food, and a Mine will usually give only +1 Minerals.  Even a Rainy/Flat (2/0/0) would merit consideration for converting to a 1/2/1 Forest tile, since you want to build Colony Pods and get more research quickly.
 * They spread automatically. So a few turns of work for Formers can become a vast forest spread over your territory later in the game, greatly magnifying the small amount of work your Formers did.
 * They can spread into and displace Fungus, removing a risk in your territory --- your units can see into Forests, they can't see into Fungus, and early in the game Forests give you a lot more resources than Fungus does.
 * They are compatible with Sensor Arrays, which provide defense bonuses to you.
 * When you have to remove them (for example to create a Farm on a Rainy/Rolling tile, or a Thermal Borehole) they get converted to 5 minerals sent to the base of the Former that removed them.
 * With Tree Farms they become well-balanced 2/2/1 tiles, and with Hybrid Farms they become excellent 3/2/2 tiles.
 * They have no ecological damage.
 * While a Mine on Rocky terrain gives you 4 minerals, a Thermal Borehole on the same terrain gives you 6 minerals and 6 energy. The technology that removes the 2-mineral limit, Ecological Engineering, is the same technology that allows you to build Thermal Boreholes, so there is usually very little reason to have Mines at all --- if you need both Food and Minerals, Forests are usually better.  The only exception is a Mineral Resource Bonus on a Rocky tile --- the bonus unlocks the resource limit even without the tech, so you can get 6 minerals from that tile early in the game.  But converting the Mine to a Thermal Borehole later is still better.
 * Condensors cause ecological damage only if they are within the workable radius of a base. You can encircle a large Arid area in your territory with bases on Moist and Rainy terrain, then build Condensors in the middle of the Arid area, just outside the workable radius of all the bases, letting their effect "leak" into the outermost ring of tiles that the bases can actually work.  Later you can add Farms and Soil Enrichers to the Condensor parks, then send Supply Crawlers to them for more food.
 * Tree Farms reduce the ecological damage of terraformed tiles, and Hybrid Farms eliminate the ecological damage completely. Thus they are useful if a base is working 3 or more Thermal Boreholes (it's possible to have up to 6 Thermal Boreholes in the workable area of a base).