Interesting work, Strategos.
I'm currently hammering out the following:
Economy
The economy has been completely retooled from previous NESes, so you may wish to pay attention here.
Economy is mostly produced on a local level. There are various types of economy, of course: agricultural, industrial, and trade. Each of these is taxed (the rate is set by, naturally enough, you), and the revenue generated from these taxes (minus that which is skimmed off by corrupt collectors) eventually ends up giving you a certain amount of money to play with.
PRODUCTION
Production is essentially all industrial and artisan activities in your nation everything besides agriculture and trade/services. It is limited by the amount of labor and resources you have: you need power to run industrial factories. In the ancient era, of course, things are rather easier to set up and maintain; however it takes a great deal to get a proper industrial economy started up. This will be a relatively minor sector until the era of steam.
AGRICULTURE
Agriculture is probably the most important part of the economy in the early eras... in fact, it will remain that way until the Industrial age, and even then, you need it to feed your people. The amount of money you can make off of agriculture is limited by the area you are growing in (this is, of course, represented by climate). Agriculture takes a long time and a lot of money to get started, and if you push it too hard, soil exhaustion is entirely possible. Note that advances can greatly improve yield: the moldboard plow, three field system, nitrate fertilizers, and so on.
TRADE
All trade is based on specialization, supply, and demand. Specialization refers to a nation producing what it is best at producing. Honduras, for example, is prime banana country, whereas Saudi Arabia would do best investing in oil. Supply is what a nation produces. Demand is what it needs.
Supply and Demand are listed on a national level. All regions trade goods are summed to create the Quantity Supplied; all regions needs are summed as Quantity Demanded.
In early eras, trade will be physically conducted through major cities Trade Centers. These are large urban areas, typically serving more than one nation. Unless you set an embargo on goods from a specific TC, your merchants will automatically trade with the nearest ones. These cities gain a bonus to their income from intraregional trade that passes through them, and in later eras will begin to see investments flow through them, along with the setup of service businesses as additional bonuses.
Provinces and cities will make money through selling their goods to these trade centers (in practice, that is; in theory theyre just conducting them through the region). The money made off of these sales appears as taxable revenues in the Province section under Trade.
Occasionally, as a player, you may facilitate the creation of a TC. This is usually done by making yours the exclusive first port of call for some trade route; to do this, youll need to set up a trade route. In order to accomplish this, you have to firstly map the route (if you dont do this quite thoroughly, you may well end up losing merchants at sea or in a desert), secondly establish it (sometimes necessitating the agreement of the country on the other end to trade), and thirdly ensure its safety from pirates and bandits.
Some trade goods give additional benefits. Luxuries will improve your peoples loyalty (in the ancient ages, usually only the rich will experience this boost). Coal and oil, as you might have guessed, are necessary for the workings of your production. Some nations need grain to avoid utter starvation.
TAX RATES
Each of these economies ends up giving you a tax base from each province and city. This tax base is (hopefully) a large number; as the leader, you can only take a part of it. This is levied through a tax rate.
There are two primary tax rates you will have to deal with.
The first is the tax for each province or city. These can, theoretically, be levied individually, or you can simply set a blanket tax rate over the entire nation. As a ruler, your objective will be to ensure that taxes are not high enough to starve your people, but still high enough to keep your nation functioning. Keep an eye on the loyalty stat.
The second set of taxes are tariffs. Now, in real life, you can play with tariffs quite a bit. For simplicitys sake, we will limit it to a single rate; a specific tariff on an item can be represented by a quick decrease in the importation of that item. Tariffs are the only way in the ancient age to make money off of trade. As in real life, therefore, free trade zones dont make any sense whatsoever in the early periods.
Keep in mind that high domestic taxes can be a bad idea. For one thing, they can lead to rebellion. For another, they can stifle economic growth. Tariffs, on the other hand, are necessary for trade, but if they are too high, trade simply will not exist. Moreover, in later eras, the tariffs from province to province can lead to stunted development, as people have little incentive to trade or develop a modern economy.
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It's rather lacking on specifics at the moment; this is mostly a concept outline. Not even a proofread one, for that point.
For the record, I fully intend to have this a visible system, with any formulas out in the open. While black boxes work well in some regards, I want to make a flexible ruleset that will work for all mods, and excluding them from seeing it seems silly to me.