The Incas focus on rushing and specialized counterunits.
The Incas are a versatile civilization as they have several useful economic bonuses. Houses provide extra population which can be very useful for quickly increasing population and saving wood. Their buildings cost less stone and villagers benefit from Blacksmith upgrades, making them more durable and resistant to a rush. These two bonuses allows the Incas to make good fortifications and forward bases near the opponents for a rush. Their extra llama bonus can be use for exploring in early game or just for taking some extra food. Their team bonus allows for farms to be built more quickly. This is especially useful in mid and late game when the economy of the team rely in farms for gathering food.
Like the other Meso-American civilizations, the Incas lack cavalry and gunpowder units, which puts them at a disadvantage in the late game. While Eagle Warriors make decent cavalry substitutes in the Castle Age and early Imperial Age, they don't have a lot of HP so are easily outmatched by Paladins and they cost a lot of gold, unlike Hussars. So in late game they must rely almost entirely on their unique units which are both individually weak and must be used in large groups to be effective.
The Incas lack any offensive or defensive bonuses for their troops so are vulnerable in pitched battles. This vulnerability is increased by the lack of durability of their unique units. This puts the Incas at a disadvantage in large battles as they lack staying power. To compensate this they must stay near to their fortifications or take advantage of the map if they can, or simply avoid frontal battles in the late game.
The Incas are probably weakest when going toe-to-toe against the Aztecs and Mayans, since the Incas' economy bonuses and Eagle Warriors are the weakest of the three Native-American civs. Additionally, the Inca's unique unit, the Kamayuk, won't shine as it won't be fighting any hostile cavalry.
Incas have a slightly different start from other civilizations. Only one house needs to be built (although two can be built optionally) and they can start gathering food immediately due to starting with a Llama. Incas have two main strategies. A Tower Rush (trush) which is made especially potent by their stone bonus and Villager bonus, and a standard Fast Castle.
For a Tower Rush, the player must go up to the Feudal Age on 22 population (21 Villagers) and task at least two to mine stone. In the Feudal Age, he or she must build a Blacksmith as soon as possible and research Scale Mail Armor in first place, then he or she must get Forging afterwards if they can afford it without disrupting Villager production. While doing this, the player need to send up to five Villagers over to the opponent's base in order to build a tower at a short distance away from their first disruptive tower. This first Tower is meant to not be spotted as it goes up, and to protect the Villagers while they make the second one, which should go over the main Gold Mine or main Forest or some such critical supply area. From here, the player must keep pressing in and building Towers within range of each other to cover all of the critical resources. If the Villagers are attacked by other Villagers, they do have Blacksmith upgrades and can take down the enemy villagers, but even so is better to only engage under a Tower, since losses should be kept to a minimum. If they are attacked by enemy military, the player must take their villagers and garrison to the tower since they are still weak vs military units.
For a Fast Castle, there is no real difference besides needing fewer Houses. Upon reaching the Castle Age, army composition is dependent on what the enemy is doing. Kamayuks counter Cavalry, especially when massed, Slingers counter Infantry, especially when massed, Skirmishers and Eagle Warriors counter Archers.
The player must try to not use too many Eagle Warriors unless he or she need to raid an enemy location, since Incas arguably have the worst Eagles in the game. Aztec and Mayan Eagles get huge attack and health boosts, respectively. Incan Eagle Warriors get a armor boost, which can help absorb arrow fire (which they already resist heavily) can reduce damage when retreating from Cavalry (Mayan Eagles can take nearly two hits for every one hit others can, so they're still inferior in this aspect) and can catch slower units easier, which is still overshadowed by Aztecs dealing extra damage.
In the Imperial Age, Incas begin to struggle. All of their troops have fairly low health, and cannot last long. They have two choices: End it in one quick strike, or prepare for a drawn out siege. Fortunately, Incas seem to be practically built for lengthy sieges. Their Villagers can take a lot of abuse before dying, allowing them to easily set up cheaper Castles on the front lines along with other ofensive buildings and military buildings such as Archery ranges, Siege Workshops, Monasteries and Barracks. Also set up Monasteries, in Imperial Age as this required for a good Inca army composition which consists of several siege units, skirmishers and archers, and some Monks for support the frontlines of Slingers, Eagle warriors and Kamayuks.
On the sea, the lack of Cannon Galleons puts Incas at a distinct disadvantage. They should either use boats more defensively, or try to keep the foe from getting any Towers or Castles up. In team games, they can simply have a teammate that take care of opposing Castles, and support them by keeping enemy Boats away.
Defensively, Incas fare reasonably well. Their Stone Walls cost 1 less stone (4 instead of 5), which helps make Stone Walling more affordable. Their dedicated counter units are good for destroying poorly composed enemy armies, and can easily retreat for healing, which is their main problem in pitched battles outside the opponent's base.
Strategy Changes in The African KingdomsEdit
Incas are greatly improved in this expansion, as all Native American Civilizations they can now create their Eagle scouts since Feudal age making an Eagle scout rush a viable option. They also receive Thumb Ring and the Slinger no longer require a Castle making possible for the Incas to perform a Slinger rush once they reach Castle Age. Also they receive Guilds and Block Printing making their economy and their Monks more valuable
Incas are valuable allies not only for their team bonus but also for their stone discount bonus on their buildings as they can create defensive structures to support all their team cheaper than other civs. Their team bonus (farms are created faster) is specially useful for civilizations that have other bonuses for farms like in the case of the Chinese (having these 2 civs on the same team boost the farms greatly from their team bonuses), the Slavs, the Mayans, the Teutons, the Spanish (that their workers create buildings faster) and the Franks.
Incas benefits greatly from civilizations that can cover their natural lack of cavalry while also they benefit from many team bonuses that helps them in a tactical way or boosts archers and infantry. allied with Slavs will help them to make housing even more affordable as the slav bonus makes military buildings to support 5 population so the Incas can increase their population capacity even faster. The Italian team bonus is also specially useful as Condottieri from them can sinergize with the Slinger and the Kamayuk in the battlefield. Alternatively, Berber teammates grant the Incans Genitours with full blacksmith upgrades as the cavalry contigent they direly need, plus Kasbah upgrade to help them amass Kamayuks and Trebuchets quickly.
Team bonuses that boost archery range units are specially useful for the Incas (like Britons team bonus, Saracen team bonus, and Magyar Team bonus) as the Slinger is considered an archer and is produced at the Archery Range.
Mayans and Incas have a very strong defensive synergy due to the Mayan team bonus and the Mayan bonus of generating extra resources from nature gathering, when allied with mayans, Incas stone walls only costs 2 stone (1 less stone than the mayans which stone walls costs 3), and mayans in this case can specialize in economy and tributing stone to the Incas, while their Inca ally builds most of their defensive structures for both players.
Southeast Asian civilizations can also provide Cavaliers, Battle Elephants and Bombard Cannons as supporting contigents. Burmese allies allow Incan players to dispatch troops to occupy nearby relics rapidly, while Khmer allies can amass real Hand Cannoneers and provide enhancements for Incan Scorpions's attacking range as more competent ranged support. The Vietnamese also grant the Imperial Skirmisher upgrade to the Incans, thus enriching their counterunit roster against most units, the Vietnamese ally can also address to their Incan ally, the locations of the opponents since the start of the game enabling to perform better a rush and for the late game with gold subsidy from Paper Money will help to create steady armies of Kamayuks, Slingers and Eagle Warriors.