Gameplay (Civ4)

== Diplomacy ==
Diplomacy in Civilization IV generally involves the trading of goods. Different trade options require different advancements to unlock, and some things may only be traded for certain other things (e.g., per turns deals must be compensated by another per turn deal). Players may trade technologies, resources (including luxuries such as Wine), maps (to reveal information about the rest of the world), and gold. Advanced diplomacy options include the creation of trade embargoes, the promising of military aid, and the adoption of particular civics and/or a religion.
The reasoning behind diplomacy is more transparent when compared to Civilization III: the Diplomacy window now displays not only the other leaders' attitudes (gracious, friendly, pleased, cautious, annoyed, furious), but why they feel that way (e.g., "-2: You refused to stop trading with our worst enemies!"). When a leader is friendly or gracious towards one's civilization, they are more likely to accept deals without unfair bargaining.
Another new feature is the new abilities of the United Nations. The United Nations wonder allows passing global resolutions (e.g., the Nuclear Non-Proliferation Treaty) in addition to granting access to diplomatic victory. Unlike real-world resolutions, Civilization IV's resolutions are binding, except for in Beyond the Sword, in which you have the option of defying resolutions.
== Combat ==
Units no longer have separate attack and defense values. Instead, they have a base strength that is increased or decreased depending on the situation. The unit's strength also affects how much damage it can do. Prior to the 1.52 patch, the unit's damage was calculated using its current strength (which also acts as life/hit points and changes accordingly). After the patch, the damage is calculated from the base strength - this means that badly damaged modern units can still easily win battles against obsolete units. Instead of generic increases in rank, individual units gain specific types of combat experience, such as bonuses against specific types of enemies or abilities like faster movement in forests. In total, there are 41 different types of unit promotions. It is also now possible for players to examine "combat odds" before attacking, giving the player a good sense as to whether a given attack will succeed or not, factoring in all the various bonuses and penalties associated with terrain, unit capabilities, and so forth.
The 1.61 patch brought further changes, and now damaged units attack or defend with the average of their current and full strengths.
== Production and trade ==
The game features 32 types of resources, all of which are tradeable and require a tile improvement (such as a Mine or a Well) to be utilized. Some resources are required for certain units, buildings, or wonders (Iron, Copper); some may double the production speed of a certain wonder (Marble, Aluminum); and some act as luxuries like in Civ III, providing either happiness or health to all cities connected to them (Fur, Dye, Incense). There are also three types of culture goods provided by World Wonders, rather than resources, that can be traded: Hit Singles, Hit Movies and Hit Musicals. To trade goods or to send them to other cities within one's borders, they must have some form of connection between the goods and the city. In the later game, this connection can be through ocean tiles, but in the early game, it is limited to roads and rivers. Cities on the same river or (with Fishing) coastline are automatically connected for trading purposes.
Production (also - as it was in Sid Meier's Colonization - known as "Hammers," the icon that represents it) is sometimes used as a resource-term on Civilization. Each tile provides a city with a certain number of "Hammers", which collect up in the city to produce buildings and units. Unlike in Civilization III, the player is no longer able to transfer all production from one project to another, but all production on a certain project will remain. For example, if the player is building a temple but decides to switch to a harbor, production on the harbor will have to start from scratch. However, the temple stays in the building queue and retains its previous progress, aside from some decay over time. As an ancillary rule, if one culture is building a World Wonder but another empire completes it first, the losing culture is compensated with gold proportional to the amount of Production points lost.
== Religion ==
The concept of separate religions is new to Civ4. In previous games, players could build Temples and Cathedrals, but the religion was just a generic feature of happiness and culture. There are now seven distinct religions in the game - Buddhism, Christianity, Confucianism, Hinduism, Islam, Judaism, and Taoism. For reasons of political correctness, there are no bonuses or traits specific to any religion, except that each religion is tied to a specific technological advance, and the four later religions (Christianity, Confucianism, Islam, and Taoism) begin with a free Missionary unit for reasons of game balance. If a player is the first to discover a certain religion on the tech tree, they can "found" the new religion; a city with no religion or the newest city in that civilization's empire becomes that religion's holy city. The player can then build Monasteries and train Missionaries to spread their religion(s) to other cities, both foreign and domestic. (Sid Meier's Colonization also has Missionaries, which spread their version of Christianity.)
Religion factors into a number of existing game mechanics. Civs that share a common state religion will be friendly in their diplomatic dealings; conversely, civs with differing state religions will be hostile to each other. Securing an open-borders agreement, sending in Missionaries and then encouraging the other civ to convert is a relatively painless way of encouraging international tranquility. The founder of a religion also receives an economic benefit: if that civ expends a Great Prophet at their religion's holy city, they will receive that religion's most sacred building (the Kashi Vishwanath, the Church of the Nativity, etc.), which provides a 1-gold-per-city tithe from every city hosting that religion. Finally, if a civ has 1) a state religion, 2) that religion's holy city and 3) that religion's sacred building, they will receive line-of-sight in every city hosting said religion, providing additional intelligence and a good way to keep an eye on foreign progress.
The new civics model of government also has a strong effect on religion: players can found a state religion, declare religious freedom, or take other actions that have profound impacts on the religious lives of their subjects. If a civilization has no declared religion, they are exempt from all described bonuses and penalties.
== Civilizations and leaders ==
Eight of the eighteen civilizations have two leaders. Each leader offers bonuses based on what conditions were exceptional during the historical reign of that leader, and each leader acts as differently as if they were a separate civilization and have distinct personalities. Several historic figures not used in previous Civ games are AI leaders in Civ4, including: Asoka, Cyrus II, Franklin D. Roosevelt, George Washington, Hatshepsut, Mansa Musa, Kublai Khan, Peter the Great, Qin Shi Huang, Saladin (though he was a hidden leader in Civilization II), and Queen Victoria.
All civilizations have some element of uniqueness and all leaders have certain traits based on their achievements in real life. While these are limited, they have some effect on a player's game plan. All civilizations also have a unique unit which can be military (such as Persian Immortals) or economic (such as Indian Fast Workers). Below is a summary of the unique features of each civilization.
Civilization	Starting advances 	Unique unit 	Leaders 	Leader traits 	Favorite Civic 	Capital
America 	Fishing, Agriculture 	Navy SEAL (replaces Marine) 	Washington 	Financial, Organized 	Universal Suffrage	Washington
America 	Fishing, Agriculture 	Navy SEAL (replaces Marine) 	Roosevelt 	Industrious, Organized 	Universal Suffrage	Washington
Arabia 	Mysticism, The Wheel 	Camel Archer (replaces Knight) 	Saladin 	Philosophical, Spiritual 	Theocracy 	Mecca
Aztec 	Mysticism, Hunting 	Jaguar Warrior (replaces Swordsman)	Montezuma 	Aggressive, Spiritual 	Police State 	Tenochtitlan
China 	Agriculture, Mining 	Cho-Ko-Nu (replaces Crossbowman) 	Mao Zedong 	Philosophical, Organized 	State Property 	Beijing
China 	Agriculture, Mining 	Cho-Ko-Nu (replaces Crossbowman) 	Qin Shi Huang 	Industrious, Financial 	Police State 	Beijing
Egypt 	Agriculture, The Wheel	War Chariot (replaces Chariot) 	Hatshepsut 	Spiritual, Creative 	Hereditary Rule 	Thebes
England 	Fishing, Mining 	Redcoat (replaces Rifleman) 	Victoria 	Expansive, Financial 	Representation 	London
England 	Fishing, Mining 	Redcoat (replaces Rifleman) 	Elizabeth I 	Philosophical, Financial 	Free Religion 	London
France 	Agriculture, The Wheel	Musketeer (replaces Musketman) 	Louis XIV 	Creative, Industrious 	Hereditary Rule 	Paris
France 	Agriculture, The Wheel	Musketeer (replaces Musketman) 	Napoleon Bonaparte 	Aggressive, Industrious 	Representation 	Paris
Germany 	Hunting, Mining 	Panzer (replaces Tank) 	Frederick II the Great 	Creative, Philosophical 	Universal Suffrage	Berlin
Germany 	Hunting, Mining 	Panzer (replaces Tank) 	Otto von Bismarck 	Expansive, Industrious 	Nationhood 	Berlin
Greece 	Fishing, Hunting 	Phalanx (replaces Spearman) 	Alexander III the Great	Aggressive, Philosophical	Hereditary Rule 	Athens
Inca 	Agriculture, Mysticism	Quechua (replaces Warrior) 	Huayna Capac 	Aggressive, Financial 	Hereditary Rule 	Cuzco
India 	Mysticism, Mining 	Fast Worker (replaces Worker) 	Mohandas Gandhi 	Industrious, Spiritual 	State Property 	Delhi
India 	Mysticism, Mining 	Fast Worker (replaces Worker) 	Asoka 	Organized, Spiritual 	State Property 	Delhi
Japan 	Fishing, The Wheel 	Samurai (replaces Maceman) 	Tokugawa Ieyasu 	Aggressive, Organized 	Mercantilism 	Kyoto
Mali 	Mining, The Wheel 	Skirmisher (replaces Archer) 	Mansa Musa 	Financial, Spiritual 	Free Market 	Timbuktu
Mongolia 	Hunting, The Wheel 	Keshik (replaces Horse Archer) 	Genghis Khan 	Aggressive, Expansive 	Police State 	Karakorum
Mongolia 	Hunting, The Wheel 	Keshik (replaces Horse Archer) 	Kublai Khan 	Aggressive, Creative 	Hereditary Rule 	Karakorum
Persia 	Agriculture, Hunting 	Immortal (replaces Chariot) 	Cyrus the Great 	Expansive, Creative 	Representation 	Persepolis
Rome 	Fishing, Mining 	Praetorian (replaces Swordsman) 	Julius Caesar 	Organized, Expansive 	Representation 	Rome
Russia 	Hunting, Mining 	Cossack (replaces Cavalry) 	Catherine II the Great 	Creative, Financial 	Hereditary Rule 	Moscow
Russia 	Hunting, Mining 	Cossack (replaces Cavalry) 	Peter I the Great 	Expansive, Philosophical 	Police State 	Moscow
Spain 	Fishing, Mysticism 	Conquistador (replaces Knight) 	Isabella I 	Expansive, Spiritual 	Police State 	Madrid
== Technologies ==
As in prior versions of Civilization, there are technologies for the civilizations to discover. There are a total of 85 technologies in the game, up from 80 in Civilization III. Technologies have many uses; they can be used for trade, for the construction of new buildings and wonders, for the founding of new religions, or for the development of new forms of government. To discover modern technologies, it is first necessary to discover the technologies that lead up to it (for example, Democracy can only be discovered after the Printing Press).
Technology development is flexible: certain technologies can be discovered in more than just one way. The game has a very useful tech tree, which can be accessed by pressing F6 on the keyboard. The tech tree displays all the techs in the game and their relations with one another. It is possible to select even unavailable techs for research. This will cause all the prerequisite techs to be researched in order. If multiple paths lead to the target tech, the civilization will pick the shortest. The final tech or group of techs, as in previous versions, are called "Future Tech", followed by a number. Instead of simply adding on to the final score, however, as in earlier games, each city receives a happiness and health bonus for each Future Tech discovered.
In single-player games, the discovery of each tech during the game is accompanied by a famous quotation from history which is voiced by Leonard Nimoy of Star Trek fame. The sources of the quotes range from the Buddha, Charles Darwin, Brillat-Savarin, Steve Wozniak, Henry Ford, the Bible all the way to Lonnie Donegan, and Dan Quayle.
== Scoring system ==
In Civilization IV the leadership skills of players are compared to a subjective list of twenty of the best or worst leaders in history, similar to the list in Sid Meier's Civilization. The score is based on a number of factors, including military growth and success, technological advancement, construction of wonders and economic growth.
The released version of the game abandoned Civilization III's graded scale. In Civ3, a spectacular victory on the easiest difficulty would provide the player with only a middling score, and the best titles were only awarded to players attempting the hardest difficulties. The original Civ4, on the other hand, allows the player to obtain any score on any difficulty level. As of the v1.61 patch, the grading system has returned to the curved-by-difficulty scale.
== New features ==
Many aspects of Civilization IV are new to the series (though some appear in spinoffs or Colonization). Gameplay innovations include:
* "Great People" that fall into five categories: Artists, Merchants, Prophets, Engineers, and Scientists. Each of these grants several bonus abilities. Among the Great People included are Aristotle, Plato, Moses, William Shakespeare, Ramakrishna, Michelangelo, Isaac Newton, Albert Einstein, and Marie Curie. (See List of historical figures in Civilization IV for a full list of people and cultures used in Civilization IV.)
* The founding and spreading of religions and the adoption of a state religion (see above).
* Instead of subtracting from a city's population upon completion, Settler and Worker units require the city to suspend its population growth, on the theory that all its new citizens are being funneled into the unit, until it contains enough people to depart. This makes Settlers significantly more difficult to build in small cities, and encourages players to build up their cities before expanding.
* The concept of city maintenance replaces corruption, which has been removed. Civilizations with a large number of small or ineffective cities will find their empire too expensive to maintain.
* One civilization's units cannot cross another civilization's territory unless the civilizations are at war or have agreed to an open borders treaty, though there are special units (such as the Spy and the Caravel) which are able to cross borders with or without the open borders agreement. 
* Governments have been replaced with a more flexible "civics" model, where the player can set the amount of freedom the citizens have (slavery, free speech, etc.). There are five different categories in the new civics model (Government, Legal, Labor, Economy, and Religion), and five separate options within each category. This appears to be adapted from the Social Engineering section of Sid Meier's Alpha Centauri.
* AI civilizations no longer act as if they have knowledge of the entire map. (In Sid Meier's Civilization and Civilization II they appeared to have only limited knowledge and could exchange maps.)
* The AI is more intelligent. It makes full use of all options and exhibits better long-term planning abilities.
* Barbarians now form cities, often named after their tribe or culture (Hun, Visigoth, etc.). These cities act and react like any other city: they send out Worker units to improve terrain, can be captured or razed by military force, can be culture-flipped, and so on. However, they cannot be contacted via diplomacy. (In earlier games, barbarians could capture cities.)
== See also ==
* Gameplay in other games
Category:Civilization IV
Civ4