The original Internet backbone was the ARPANET.
In 1989 the NSFNet backbone was established, the US military broke off as a separate MILNET network, and the ARPANET was shut down.
A plan was then developed for first expanding NSFNet further, prior to rendering it obsolete by creating a new network architecture based on decentralized routing. (to be written: creation of the NAPs, EGP)
With the decommissioning of the NSFNet Internet backbone network on April 30 1995, the Internet now consists entirely of the various commercial ISPs and private networks, as connected at their peering points.
The term "Internet backbone" is now sometimes loosely used to refer to the inter-provider links and peering points. However, with the universal use of the BGP routing protocol, the Internet functions with no single central network at all.
With the advent of the dot-com bust of 2002, a number of major telecommunications carriers are threatened by bankruptcy, and some failed completely: for example, the EBONE network was decomissioned in its entirety. This was a successful test of the level of fault-tolerance and redundancy of the Internet.
See also: