I'd just like to take a moment to air a pet peeve of mine in game design: the inclusion of money as a resource in many empire-builders.
Money can go by many names. It can be gold in the goblin kingdoms, dollars in the industrial age, or energon crystals in the distant future. What it is, in game mechanics, is a universally exchangeable good, often with special properties of its own which no ordinary good can imitate. Running short of steel for your armies or silks for the privileged classes? Just head down to the local market and part with your hard-earned gold to get some. That's the way money has always worked for you, right? If you want some groceries, a new television, office supplies, as long as your wallet is full or your credit good, you can buy some locally.
The problem is, money doesn't always operate the same way for grand empires as it does for individuals, but game designers, used to thinking of money like an individual, don't always stop to realize it.
The difference is whether a system is open, meaning material passes between the system and an external pool, or whether the system is closed, meaning it doesn't. For example, your car has an open atmosphere; air passes readily in and out. A space station has a closed atmosphere; air inside stays inside, and if there were any air outside, it would stay outside.
Some games, like Railroad Tycoon, have open economies. Your company doesn't control all the steel foundries or coal mines you need to keep your rails running. Those resources come from sources outside the game. You pay for the coal and steel with money collected from your passengers, another element whose inner workings lie outside the game model. This is all well and good. In an open system, money is not only acceptable, but desirable game design, a powerful tool for abstracting behavior which would make the game more complex without adding anything interesting for the player.
For a game like Civilization, however, you represent the entire state and its resources: oil, timber, food, labor, communication, social attitudes, the works. Your economy is closed, except insofar as you trade with a very limited number of like nations. Money, especially when it is a poorly defined mishmash of ?other resources we haven't explicitly included,? leads to some awkward situations. Here are a few examples.
In Civilization, when you scrap an SDI complex for 200 gold, to whom do you sell it? Presumably not to your neighbors, who might still be working out the secret of gunpowder. But it's difficult to imagine your citizens needing to protect their house from the Jones's nuclear warheads. Perhaps the gold represents, not actual bank credit, but a collection of raw materials that go into an SDI complex ? but then, how can you spend the concrete and electronics to rush production on a paratroop division? Last I checked, the 82nd airborne didn't consider cinderblocks standard issue.
In Imperialism, money is a necessary ingredient to several functions, including conscription and rail-building. If your bank account runs low, you can have all the steel, lumber, coal, and labor in the world, and be unable to lay a few miles of track. How, pray tell, will a shipment of gemstones speed the creation of a rail network?
In Alpha Centauri, energy can be collected and spent to rush building projects. Okay, I can buy that: maybe high-powered tools can get the job done faster. But how can energy be turned directly into scientific advancement? Using it to help build libraries and computer centers, fine; but technical brilliance requires more than giving the labs twice as many overhead lamps. (Or is the assumption that anything but 100% devotion of energy to science means a large portion of your scientists can't turn on the lights? If so, why train such an excess of scientists, knowing half of them will be squatting in cold, dark research facilities?)
In Age of Kings, if you should run low on food but have a ready supply of gold, you can exchange them at a market. If the other players are hostile (and thus not unwilling to trade), whence does this extra food come? Farms are built and sheep slaughtered only at your command; there are no ?extra? farms stashed away somewhere to provide bread for the right price. Cities isolated by siege learn very quickly that mountains of cash won't feed anybody if there's nobody around to sell.
Again in Civilization, a city with an excess of cloth can set up a trade route with another city having an excess of cloth. Both instantly enjoy a healthy boost to happiness, income, and/or scientific progress. Why? One is put in mind of the joke about stockbrokers marooned on a desert island who become rich within a year trading shells back and forth between themselves.
Silly? You bet. So what's to be done about it? Designers must force themselves to think twice about just what money is in their games. If it's simply credit for supplying other players with materials they need, money will behave one way. If it's a reserve of labor you can draw from your own citizens, it will behave another way. If it's consumer goods, it will behave an entirely different way. Define carefully. Further, it helps to consider how the model will react to extreme settings of money. If a nation has nothing but a reserve of cash ? no food, no minerals, no labor ? what can it really do with its money? If a nation has no money at all, but heaps of actual material goods, will it be self-sufficient, or succumb to paralysis because one critical material has been abstracted as ?money?? Simply pinning a model down to a concrete meaning goes a long way toward making sure the model behaves plausibly.