If your stock of these materials is exhausted, your forces may become helpless in the face of the enemy. Mercenaries are expensive to maintain but quick to create in a pinch. Resources do not run out. Though this may not be realistic for such items as coal or gold, this is more game practical in that these resources are, to an extent, an abstraction representing many other resources of fuel and metals. More appreciated is the fact that the wood is not exhausted.
Trees grow back.
Multiplayer support Choose Multiplayer from the main menu. Later on the number went up to 61. Be aware that these kinds of servers are wide open. There is no usage policy or stated rules, so be prepared for some standard, uncivil Internet behavior and crude language. However, again, the multiplayer historical scenario played had no information about goals in the game and ended without a clear message about which side had prevailed.