As in previous versions, cities remain the central pillar of civilization gameplay. A city can be based on a site desired by a unit of settlers manufactured in the same way as military units. The city will then increase in population; Production of units and buildings; And create research, wealth and culture.  The city will also expand its boundaries by one or more tiles at a time, which is essential for the claim of territory and resources. The expansion process is automated and adapted to the needs of the city, but the tiles can be purchased with gold.   Independently developed software, known as the Giant Multiplayer Robot, uses the Hotseat multiplayer mode in Civilization V to mimic the play-by-email functionality available in previous Civilization series titles.  Maybe it`s an economic thing? In Civ 5, this would happen sometimes, but they would also ask for gold to charge the cost of the research agreement. But they don`t do it here and the cost of the research agreement has changed. So I was confused city states, a new feature in the series, are small civilizations that can interact with but are not able to achieve victory. Unlike the great powers, city-states can develop on the territory, but they never create new cities (although they can conquer other cities with military units). In addition to total conquest, great civilizations have the opportunity to befriend city-states through bribes or services. City-states offer the player bonuses such as resources and units that increase as players advance to new eras.
In the “Brave New World” expansion package, city-states give allied players additional delegates to the World Congress, which begins in industry time. There are three types of city-state in the basic game, each with different personalities and bonuses: maritime, cultured and militaristic. Two other types of city-states (mercantile and religious) have been added to the Gods-Kings expansion package to add new gameplay mechanics. City-states play a leading role in diplomacy among great civilizations, as well as concrete demands and rewards.  This may simply be my incomprehension for the detailed mechanics of Civ 5, but I thought that the research agreements were evaluated at the highest level of research between 2 civs.