Cultural ties affect diplomatic stances between players. Cultural ties are created through technology trading, sharing of civics, religion, and other cultural aspects.
From Don Pedro II's Test of Time
Unification A new unification game option creates "rival cities" around a player's capital that have the names of the cities of the player's civilization and have the same player colors, but they are run by Barbarians. The number of cities and their distance from the capital is dependent on map size, but players can be sure that they will still be able to expand without having to conquer these cities first. When a player unifies their civilization by taking these cities, they receive a prompt notifying them of their accomplishment and a new trait based on the way in which they took over their empire. Players will be able to conquer rival cities through military might, religion, diplomacy and culture.
Embassies Embassies are new tradeable items that appear in the diplomacy screen. Establishing embassies with other players provides additional information about the other player as well as being a prerequisite for signing Open Borders and Defensive Pacts.
New Tradeable Items
Workers – Players can now trade workers between each other. Workers must be in a city to be traded.
Military Units – Players will now be able to trade siege, naval, armor and air units between each other via the trade screen. Infantry and cavalry will not be tradeable because they are not hardware.
Embassies - See above New Game Concepts for details on what embassies are and how they work.
Contact - Trade contact with a third party to a player who has not yet met them. This was a feature that was in Civilization 3 and has been reintroduced.
Corporations - Trade control of corporations. A new headquarters city is picked automatically in the receiving player's empire.
Pledged Secretary General Vote - Get the other player to guarantee their votes for you in the next election for Secretary General. Once the other player has agreed, they cannot sell their vote to someone else or vote their own interest (Voided in event of war). It's not possible to trade one's vote if one is an eligible.
From White Lies Black Ops
- Terrorist Organizations introduced into the game, which may grow and spread within civilizations. Terrorism becomes a continuing problem, and civilizations may opt to become terrorist states.
- Coalitions. You may form coalitions with other civs to make a concerted military or blackops attack on more powerful civilizations. By the same token, smaller civilizations may gang up on you if you grow too strong too fast.
- Black Ops are added; civilizations may take special military operations against various civilizations. Based on my e-mails, a fan favorite.
- Internal Security options, which may be used to manage a civilization's internal affairs.
- Hostages, which may be taken when attacking a city or pillaging certain improvements. Hostages can be publicly executed (driving up war weariness in the target civ), sold back or put to work in work camps.
- Indigenous People in a civilization, who may be exploited and eventually radicalized into terrorist groups. If treated well, they can benefit a civilization through random events. If treated badly, they will radicalize into terrorists.
- Respect, in addition to like and dislike, as an element of civilization relationships.
- A handful of new units (such as the Diplomat, with new, unique abilities), buildings, technologies and terrain modifications.
New National Project: Religious School System. Raises the terrorism level in all other civilizations.