From Warzone Wiki
 Mod description
Allows players to purchase neutral territories with gold rather than conquering them by force. Requires that the game is a commerce game, and will do nothing otherwise. The game creator can configure how expensive territories are to purchase, based on how many armies are on the neutral territory. To initiate a purchase, click the button for the mod on the menu, select the territory, and a purchase order will be inserted into your orders list. The purchase will complete when the turn advances.