Creation of the Internet

The core networks forming the Internet started out in 1969 as the ARPANET, created by the United States Department of Defense Advanced Research Projects Agency (ARPA). Some early research which contributed to the ARPANET included work on decentralised networks, queueing theory, and packet switching. On January 1, 1983, the ARPANET changed its core networking protocols from NCP to TCP/IP, marking the start of the Internet as we know it today.
Another important step in the development was National Science Foundation's (NSF) building of a university backbone, the NSFNet, in 1986. Important disparate networks that have successfully been accommodated within the Internet include Usenet and Bitnet.
The collective network gained a public face in the 1990s. In August 1991 Tim Berners-Lee publicized his new World Wide Web project, two years after he'd begun creating HTML, HTTP and the first few web pages at CERN. A few academic and government institutions contributed pages but the public didn't begin to see them yet. In 1993 the Mosaic web browser version 1.0 was released, and by late 1994 there was growing public interest in the previously academic/technical internet. By 1996 the word "Internet" was common public currency, but it referred almost entirely to the World Wide Web.
Meanwhile, over the course of the decade, the Internet successfully accommodated the majority of previously existing computer networks (some networks such as Fidonet have remained separate). This growth is often attributed to the lack of central administration, which allows organic growth of the network, as well as the non-proprietary nature of the Internet protocols, which encourages vendor interoperability and prevents one company from exerting control over the network.