The common law system originally developed in England and strongly influenced the development of the American Legal System. The English common law is based on the decisions of the court. The foundation of those decisions was usage and customer rather than tomes of law. The reason for this was that in England the judges made and controlled the common law, and considered legislation as an intrusion. There was great pride in the English common law.
Now the Commonwealth countries including the United States inherited the common law legal tradition of the English law. The US courts are also common law court and have inherited some of the principles of the common law direct ...
This solution gives you a detailed discussion on English common law's influence.