These bids were developed as an extension of 2 over 1 bids.  One club is the only one level opening bid that doesn't have a 2 level bid possibility to create a game force. Even though methods have been devised to create a game force after a one club opener, the force usually doesn't occur until the two level with bids like fourth suit forcing, for example,. The game force occurs after a 1 diamond response to opener's one club, leaving plenty of room to establish suit and game or slam level. In addition, there are inferences available when responder doesn't bid 1 diamond, i.e., responder has fewer than 12 points

Basics of 1 Club/1 Diamond