Whether or not you want to make your mark through the militaristic path, you cannot ignore one thing: the economy is vital! You need resources and money to trade, recruit and maintain armies, bribe your neighbors, pay tributes, and even to improve your economy and produce some more!
Gold is the most important resource. It will be collected in two manners, tax collection on your lawful populations (outlaws do not pay taxes!) and gold mines. The amount of gold you possess is measured in ducats. In addition to those two basic revenue sources, you can earn gold by selling resources in the market, or turn to your neighbors to supply you, either through trade, tribute, gift, or simply by going there with your armies threatening them into paying!
In Economy => Resume you will see displayed your Land’s efficiency. The efficiency of a Land affects tax revenue. It depends on the Type of Land, and its size, both in territories and total populations. As a Land grows, its efficiency will slowly go down.
The amount of gold collected trough taxation is calculated in the following manner:
Taxation of a territory = Population x 0.10 x Land efficiency x (1 + City level x 0.05)
The amount of gold received from gold mines can be seen in economy => resources or in the facilities list, and depends upon the level of natural richness of such metal the territory has, and upon the Land types efficiency exploiting mines.
In Economy => Resume you will also see the income statement of the previous turn, where you can identify your revenue sources (tax collection, received tributes, mines and goods sold at the market) and how it was spent (tributes paid, facilities maintenance, military units maintenance, market expenses, facility construction and military units recruitment). Revenues minus expense will give you the surplus/deficit for the turn, which is the variation of your total gold stock from the previous turn to the beginning of the current one.
Be careful not to let your gold go to negative values, has you will automatically have to borrow money, from which you will pay a 10% interest per month! And if the value continues to drop you will eventually suffer from worst effects, which in extreme circumstances will completely cripple your Land.
When you finish the turn between minus Total Population X 0.05 and minus Total Population X 0.20, your armies will become demoralized and less battle ready,
Of course, if you go into negative money you will also not be able to do anything that requires gold, such as recruiting new units, buying resources in the market or building facilities. This happens because you cannot voluntarily borrow money. Loans will only be received to automatically cover maintenance costs.