In order to reduce congestion on the map, players will be able to perform a limited amount of unit stacking (a change from Civilization V), but will only be able to stack similar unit types or symbiotic units. For example, a warrior unit can be assigned to a worker unit to protect that unit from barbarians in the early game.
The game’s technology tree, now known as the active research system, has also been modified to help boost technology research if the player has access to appropriate improvements or resources. For example, having built a quarry will help boost the research into masonry. Technologies based on having access to water, such as sailing, would be limited if the player started in the middle of a continent. A new feature, Eureka Moments, will increase the player’s progress towards certain technologies after completing a specific in-game task: for example, discovering a Natural Wonder would contribute towards the Astrology technology improvement.
Past iterations of the game were found to be difficult to win if one chose to follow a Cultural victory route, as other victory routes, such as Technology, would nearly always outplay the cultural path. To help balance the game towards Cultural victories, a new Civics tree has been introduced. The Civics tree brings in the cultural improvements that were previously part of the technology tree in earlier Civilization games, such as Drama and Philosophy, into a separate mechanic. Culture gained from cities are used to build on the Civics tree in the same manner Science from cities build up the Technology tree. Completing certain Civics will then unlock policies towards the civilization’s government. In Civilization VI, the government is defined by placing appropriate and available policies, represented as policy cards, into a number of slots divided between Military, Economic, Diplomatic, and Wildcard categories. These define boosts or limitations for the civilization, such as improved attack bonuses for military units against certain types of enemies. These can be changed for free upon completing any Civic, or at a small cost at any other time, allowing a player on the Cultural route to adapt to a new situation as needed, according to lead producer Dennis Shirk. More advanced cards, only obtainable through significant advancement in the Civics tree, can unlock improvements that give the Cultural Victory player advantages over other players, such as reducing the time or cost of producing new units. Various choices made by the player may cause unhappiness in their population as with previous games, but in Civilization VI, many of these will be localized to the city affected by the choice rather than the entire population, further aiding towards Cultural victory-style players. The Religion system introduced in Civilization V’s Gods and Kings expansion is built further upon in VI, featuring more units and improvements that can lead to religion-on-religion conflicts.
AI opponents, represented by famous past world leaders such as Qin Shi Huang and Theodore Roosevelt, will have new agendas that will influence how the player interacts with them. Some of these will be fixed based on the leader, using historical aspects about how that leader generally behaved during their rule. For example, a player may gain favor with a civilization led by Cleopatra by showing military might against neutral barbarians. However, a second hidden agenda will be randomly assigned each game, requiring the player to discover this themselves. Espionage will now also work towards revealing these hidden agendas.