The Combine is a shady corporation that owns and operates saloons and casinos in towns along the frontier.
Agents for the Combine are buying up saloons and casinos, creating a network of vice across the western frontier. If the owners of these businesses don't want to sell, the agents use threats and blackmail to encourage the owners to relent. According to Robbie James, owner of the Tailgate Casino, the Combine turns all of these casinos crooked with fixed decks, dice and games.
Unfortunately for Robbie, the Combine has set its sights on acquiring her establishment next. (The Gamble)