as the internet was finishing up in the early 1990s, prior to the Clinton’s 1993 “National Information Infrastructure” agenda, which explicitly promoted private-sector involvement, the connection of one network to another was still a little hinky. Commercial use was still PROHIBITED until 1995 by which time they got all the kinks out and it was ready to the onslaught of commercialization.
So in this email I got in 1992, the mailing list I was on was on BITNET which had to go through a gateway to go through the Internet (under construction still) to get to me where my email was.
These networks all existed but they couldn’t all communicate with each other. It was through the creation of interoperable protocols, steered by the IETF (Internet Engineering Task Force) which still exists and was as public as stodgy committees can get (anybody can join in) that standardized communications protocols and gave DIRECTIONS any corporations that wanted to “follow along” to join the internet to use if they wanted their hardware and software to also participate in the internet.