Each "Command & Conquer" game has included the ability to play multiplayer games against other players. Each box of "Command & Conquer" contained two CD copies of the game, making multiplayer gaming possible with a single purchase of the game. Westwood Studios advertised this on the packaging with the slogan "A second copy, so you and your friend can destroy each other." This resulted in "Command & Conquer" becoming the first RTS game title to feature competitive online play, and this is considered the most pertinent outside factor in the success of "Command & Conquer". All games in the series up to "Command & Conquer: Red Alert 2" featured two CDs that could be used for this reason. Later games did not.