What was used before APIs became the standard?

Question

I’m not in the IT sector but I’m beginning to understand the logic behind sending requests and receiving responses for various reasons. What was used before APIs became the standard for communication between systems?

Edit: I understand now that I’ve been in fact asking about REST API.

In: Technology

Answer 1

owls and pigeons of course.

Seriously though, as others have already pointed out, interfaces for networked machines to communicate to each other exist in some form since there are networked machines.