Combat (Civ4)

Conflict is an integral part of human history. For as long as there have been people, there has been conflict. At first this conflict was individual - where one man fought another for food, or water, or because the first man didn't like the way the second man looked at his mate. But as human society has advanced in organization and sophistication, so has conflict. When men organized in tribes, they fought other tribes. Once the tribe's group of huts became a city, the citizens of opposing cities spent much time, effort, and energy beating each other up. And so on, up to today, when nations fight other nations on land, sea, air, and (soon) in space.
== When Combat Occurs ==
Combat occurs whenever a unit attempts to enter a space occupied by a "hostile" unit. Barbarians and animals are always hostile; other civilizations' units are only hostile if you are at with them. Unlike previous Civilization games, your units can occupy the same tile as foreign units if you are in neutral territory or have an agreement. (But see special rules for air units and invisible units.)
== Combat Strength ==
Each unit in the game has a "combat strength." When one unit fights another, the computer applies any combat strength modifiers to the units' combat strengths and then determines the odds for the combat.
=== Injured Units ===
If a unit is injured when combat begins, the computer uses the unit's injured combat strength to determine the odds.
== Combat Strength Modifiers ==
A variety of things can modify a unit's combat strength. Modifications are listed as percentage bonuses. If the unit gets more than one combat modifier, all modifiers are added together and then applied. (Example: a unit gets a 50% terrain bonus and a 25% bonus for experience. The two percentages are added together and then applied, giving the unit a final bonus of 75%.)
=== Bonuses for Combat vs. Particular Units ===
Some units get bonuses when fighting particular units. A for instance gets a 100% bonus when fighting a mounted unit. Healthy spearmen have strengths of 4; when fighting s units their strength is increased to 8.
=== Terrain Defensive Bonuses ===
 gives bonuses to many (but not all) units. A spearman being attacked while occupying a forested hillside gets a 75% bonus, raising his combat strength from 4 to 7. Units also get bonuses for defending against units attacking across rivers.
=== City Defense Bonuses ===
Certain units get bonuses for defending in cities. City buildings like provide bonuses except against gunpowder units. Culturally-advanced cities give defending units Cultural Defensive Bonuses, as well. The amount of defense a city receives from buildings and culture follows "or" logic, choosing the higher from buildings or culture to apply to units defending the city. Cities receive +20% defense at each cultural level, up to +100% at Legendary culture. Walls and Castle each provide +50% defense. However, even cities with cultural defensive bonuses higher than Walls can benefit from Walls, as Walls also reduce bombard damage from pre-gunpowder units by 50%.
=== Fortification Bonuses ===
Each turn that a unit is fortified on the same square, it gains a 5% bonus to its strength, up to a maximum of 25%. As soon as the unit moves to another tile, this fortification bonus is lost.
=== Promotion Bonuses ===
Experienced units may receive bonuses from . Promotions may add to overall strength or add to a unit's strength under particular circumstances (such as against certain unit types or when defending in certain terrains, etc.)
=== Examples ===
These combat strength modifiers can make a very significant difference when they are added together. A with combat strength 8 will almost always defeat an of strength 4 without modifiers, but the odds can change drastically under the right circumstances. If the Explorer is fully fortified (+25%) on a forested hill tile (+75%) and possesses the Guerilla II (+50% on hills) and Woodsman II (+50% in forests) promotions, the Explorer suddenly has his strength increased 200% to 12 overall! The Maceman may be in for an unpleasant surprise if he tries to attack.
s and Longbowmen are difficult to dislodge from cities for the same reason. Archers get a natural 25% city defense bonus, which can be further improved with City Garrison promotions, and can also take advantage of a city's defensive bonus from walls and/or culture. An archer that is fully fortified (+25%) in a city with walls (+50%) and has the City Garrison I promotion (+45% total city defense) will have a strength not of 3, but of 6.6! This is the reason why those pesky archers can defeat more powerful units like Horse Archers when they are protecting cities. This effect is compounded by archers' first strike ability (see below).
== Combat Odds ==
At the beginning of a combat, the computer determines the combat strengths of each unit (see above) and then determines the odds for the combat. If two units of equal modified combat strength battle, each unit has a 50-50 chance of winning each combat "round" (see below) and inflicting damage on its opponent. If one unit's modified combat strength is twice that of the opposing unit, the stronger unit has a 2-to-1 chance of winning each round and inflicting damage on its opponent.
Note that the combat odds determined at the opening of combat remain throughout the entire combat. Odds are not updated to reflect damage inflicted during a round.
===Stacked units===
If multiple units are stacked in the same square, then the computer will make the attacking unit fight the unit in that stack that has the highest combat strength against that attacker. For example: if a and are stacked and a is attacking the stack, and no unit has any promotions, the spearman will lead the defense as it's the most capable, having a strength of 8 against mounted units vs the swordsman's strength of 6.
== Combat Rounds & Damage Amounts ==
Combat is fought in rounds. During each round the computer makes a random "combat check" against the odds, and the losing side takes damage. Combat continues until a unit is destroyed or "withdraws" from combat.
The amount of damage that can be inflicted in a round is determined by the combat odds. If two equal units fight, the losing unit takes 20% damage per round. (In this type of battle, the first unit that loses five rounds will have taken 100% damage and thus will be destroyed.) If one unit's strength is bigger than the other, the bigger inflicts proportionately more damage when it wins a round, while the smaller inflicts less.
===First Strike===
Some units, whether inherently or through , have a first strike ability. If the opposing unit doesn't have this ability and isn't immune to first strikes, the unit with the first strike ability gets extra round(s) of combat. The odds of winning and losing the round are calculated the same way as normal (see below), however, the unit doing the first strike takes no damage if it loses. If both units can deal first strikes, then there is no effect on combat.
For example: a attacks a on open terrain. Since both units have a combat strength of 6, their chances should be roughly 50:50. Given that these units have equal combat strength, the first unit that loses five rounds will be destroyed. However, the longbowman has a 50% chance of inflicting 20% damage to the swordsman in the first round of combat. If it loses this round, it will have a 50% chance of winning the fight against the swordsman, but if it wins, it only needs to win four more rounds , while the swordsman has to win five more rounds. When the first strike is counted, the longbowman needs to win five rounds, whereas the swordsman has to win six. In the end, this gives the longbowman a 67% chance of being victorious. 
===Collateral Damage===
Some units are capable of inflicting collateral damage. This only comes into effect when the attacker is facing a stack of units. The main rounds of combat will proceed as usual, however, there will be an extra round inflicted to 5-8 other units in the stack. This round of combat will always result in a win for the attacker, regardless of whether the main fight is a win or loss. The damage inflicted is calculated the same way as for any other type of combat, and then halved. 
Most collateral damage units have a damage cutoff. If all the units in the stack are at or below this amount of health, then no damage can be inflicted. So, if a with a collateral damage cap of 75% is attacking a stack of four (all units have a combat strength of 4), the fight will continue until the trebuchet has lost five rounds of combat and been destroyed (33% chance), or until the trebuchet has won four rounds of combat (67% chance), at which point it will withdraw. The other three spearmen will receive one round of collateral damage and be damaged by 10%, regardless of the outcome of the main fight.
===Withdrawing===
Some units have a chance to withdraw from combat. This will only occur if the unit is the attacker and has lost a round of combat. Instead of being destroyed, the unit may instead withdraw from combat.
===Flank attack===
Some units are capable of inflicting a flank attack. This is most common when a mounted unit is attacking a stack containing siege units. In order for a flank attack to occur, the attacker must either win the fight or withdraw from combat. A successful flank attacking unit will inflict one round of combat against any siege units in the stack.
== Victory or Defeat ==
If the defending unit wins the combat, the attacking unit is destroyed. If the attacking unit wins, the defender is destroyed. If the space is now vacant, the attacker moves into the space. If other units still occupy the space, the attacker remains where it was when it launched the attack. If one unit is destroyed, the surviving unit gains experience (see ).
== See also ==
* Combat in other games
 
Category:Game concepts (Civ4)