What I found striking, when I first read the book years ago, was that the development of FTP was completed in 1972 (RFC 354). That was was the birth of the internet: the means by which files are transmitted from computer to computer over differing networks. It took 20 years from that point for the internet to enter the mainstream.
If you're interested in the history of technology and science this is a wonderful book. I was fascinated by the development of the internet as a series of distributed networks. Simply put the problem was not "how do you protect the system from attact" but how does the system survive after the attack. (Remember, in the beginning, the "internet" was a DARPA project.)
Baran's idea constituted a third approach to network design. He called his a distributed network. Avoid having a central communications switch, he said, and build a network composed of many nodes, each redundantly connected to its neighbor. ...
Theoretically it might might be possible to set up a network with numerous redundant connections ... But there was a technical limitation, since all signals on the telephone network were analog signals. The telephone-switching plan prohibited more than five links to be connected in tandem, because signal quality deteriorated rapidly with the increased number of tandem links.
At the same that Baran was developing his concept of distributed networks digital technology was coming onto the scene.
Wow! The first few chapters describing the breakthroughs were astounding.