Accredited Registrars

Originally there was only one registrar who for a period of 5 years was given an absolute monopoly on domain registration by the United States Department of Commerce. That registrar was Network Solutions. The top level domain registry had to exist as a monopoly in the beginning in order to guarantee that domain registration and domain resolution service was centralized and managed. This made many of the next developments possible, such as the World Wide Web (which couldn't exist without the Internet and a working DNS system). However, it became clear that Network Solutions was not providing adequate service and could not keep up with demand. The Shared Registry Service was created to solve these problems.

Read more here.