The core mechanics of a game determine how that game actually operates: what its rules are and how the player interacts with them. It consists of the data and the algorithms that precisely define the game's rules and internal operation. In my book Fundamentals of Game Design, Third Edition (New Riders, 2014), I introduce the concepts of resources, sources, drains, and converters. Much of that material applies specifically to CSGs, which use more kinds of resources than any other genre.
In many CSGs, the primary resource is money. Money is usually treated as an intangible resource; it is seldom seen in physical form. (Dungeon Keeper is an exception: Gold has to be mined and transported back to a treasury, and the player ...