Your kingdom may receive a small income each turn from any or all of the following (depending on your actions and their success):

1. Each troop successfully raiding a foreign province.
2. Wealth brought back by adventuring heroes.
3. Tariffs on foreign trade routes that run through provinces under your control.

Your kingdom may receive a large portion of income from:

1. Tax revenue from each province under your control.
2. Trade revenue from routes established with kingdoms abroad.