EARN and
BITNET were two large academic computer networks based on
IBM mainframes, also including many
VAX/VMS nodes.. They were joined
somewhere around 1985.
Most American universities were on BITNET; BROWNVM was an important node.
The Dutch academic network, including all universities, was part of EARN; its main node, HNYKUN11, was the general purpose mainframe at Nijmegen university.
(Note :The names are in all caps because that's how the operating systems would present them.)
IBM mainframes and VAX/VMS computers were predominant in business administration, for general purpose use, and for number crunching in non-technical areas (statistics and such). It was mainly to connect this existing computer base that EARN/BITNET were created, and it grew to immense proportions.
In computer science and related fields, Unix and the Internet were much more popular. For example, the Nijmegen computer science department operated its own TCP/IP based network of DEC and Sun hosts, but it wasn't connected to the Internet until 1990 or so.
As mainframes and VAX gave way to the PC, EARN/BITNET gradually lost its host base. Internet technology, which was free, easy to implement, and designed for peer-to-peer networking between massive numbers of hosts, was rapidly taking over by 1990.