My previous hands-on report with Civilization V indicated that I felt pursuing diplomatic relationships with the new city-states to be underpowered relative to other ways to spend your resources. A few thousand years in Alexander the Great's shoes has taught me otherwise.
First things first, for those of you not up to speed on Civ V: City-states are minor nations that never expand, but will defend themselves and can be befriended by major civilizations. When you're allied with a city-state (which takes a 500 gold buy-in and 250 gold every 30 turns to maintain the relationship, though those numbers can be modified by various things as you'll see in a minute), they'll send you any luxury or strategic resources they have and help you out depending on what sort of state they are. Maritime states send food to each of your cities every turn, cultural states add culture to your civilization, and military states occasionally gift you units.
The baseline benefit doesn't sound that good on paper. After all, 250 gold can be a lot of things: An instant worker unit, a research agreement with a rival, a few hexes brought into your city borders, or more. Thirty turns of a luxury resource (all city-states spawn near one, and sometimes will expand their borders to control a second or possibly a strategic resource like iron or horses) and a little food or culture or a single unit isn't that great, especially considering that it's not a permanent bonus and it can all be for naught if a rival conquers the city-state. On the other hand, you can make it work for you with a little effort. Allow me to explain.
Alexander's trait is the Hellenic League, which makes his influence with city-states degrade at half the normal rate. Right out of the gates, Greece gets 60 turns of alliance per 250 gold rather than the typical 30, significantly altering the equation. Furthermore, the Patronage social policy*, which is available starting in the medieval epoch, grants several more city-state bonuses, and is worth a deeper look.
*Civ V's social policies are a replacement for Civ IV's civics. These permanent choices are unlocked by accumulating culture through constructing buildings like Temples in your cities, and by allying with cultural city-states. You get to pick a new social policy every X amount of culture generated, where X depends on the number of cities you have and how many policy picks you've already gotten. Each policy branch – Tradition, Honor, Patronage, Rationalism, etc. – has several sub-branches, each of which cost a pick on their own. Maxing out the Patronage branch, for instance, costs a total of six picks – which is something like 100 turns of cultural development, even if you're focusing on it.
(Next up: The power of Patronage)