The term "Application Program Interface" first appeared in a paper called Data structures and techniques for remote computer graphics presented at an AFIPS (American Federation of Information Processing Societies) conference in 1968. It was used to describe the interaction of an application with the rest of the computer system.

In 1974,history of apis was introduced in a paper called The Relational and Network Approaches: Comparison of the Application Programming Interface. APIs then became part of the ANSI/SPARC framework. It's an abstract design standard for DBMS (Database Management Systems) proposed in 1975.
By 1990, the API was defined simply as a set of services available to a programmer for performing certain tasks. As Computer Networks became common in the 1970s and 1980s, programmers wanted to call libraries located not only on their local computers but on computers located elsewhere.
In the 2000s, E-Commerce and information sharing were new and booming. This was when Salesforce, eBay, and Amazon launched their own APIs to expand their impact by making their information more shareable and accessible for the developers.
Salesforce, in 2000, introduced an enterprise-class, web-based automation tool which was the beginning of the SaaS (Software as a Service) revolution.
eBay's APIs in 2000 benefited how goods are sold on the web.
Amazon, in 2002, introduced AWS (Amazon Web Services) which allowed developers to incorporate Amazon's content and features into their own websites. For the first time, e-commerce and data sharing were openly accessible to a wide range of developers.
During this time, the concept of REST (Representational State), a software architectural style, was introduced. The concept was meant to standardize software architecture across the web and help applications easily communicate with each other.
As time passed, APIs helped more and more people connect with each other. Between 2003 and 2006, four major developments happened that changed the way we use the internet.
In 2003, Delicious introduced a service for storing, sharing, and discovering web bookmarks. In 2004, Flickr launched a place to store, organize, and share digital photos online from where developers could easily embed their photos on web pages and social media. These two quickly became popular choices for the emerging social media movement.
In 2006, Facebook launched its API which gave users an unpredictable amount of data from photos and profiles information to friend lists and events. It helped Facebook become the most popular social media platform of that time. Twitter, in the same year, introduced its own API as developers were increasingly scraping data from its site. Facebook and Twitter dominated social media, overtaking the population of which APIs were the backbone. At the same time, Google launched its Google Maps APIs to share the massive amount of geographical data they had collected.
By this time, the world was shifting towards smartphones, people were engaging more and more with their phones and with the online world. These APIs changed the way how people interacted with the internet.
In 2008, Twilio was formed and it was the first company to make API their entire product. They had introduced an API that could communicate via5 phone to make and receive calls or send texts.
In 2010, Instagram launched its photo-sharing app which became popular within a month as social media was booming. Later, as users complained about the lack of Instagram APIs, they introduced their private API.
By this time, developers had also started to think of IoT (Internet of Things), a way to connect our day-to-day devices with the internet. APIs started to reach our cameras, speakers, microphones, watches, and many more day-to-day devices.
In 2014, Amazon launched Alexa as a smart speaker which could play songs, talk to you, make a to-do list, set alarms, stream podcasts, play audiobooks, and provide weather, traffic, sports, and other real-time updates as you command.
In 2017, Fitbit was established which delivered a wide range of wearable devices that could measure our steps count, heart rate, quality of sleep, and various other fitness metrics. It connected our health with the cloud.
As we began connecting increasingly with the internet, privacy and security concerns started to show up. The year 2018 was the year of privacy concerns. People started to think about their data being shared among large organizations without their permission and it could be misused.
An example of users' data being misused could be Facebook's API when one developer discovered that they could use their API to create a quiz that collected personal data from Facebook users and their friend networks and then sold that data to a political consulting firm. This scandal exposed the Dark side of APIs. This made users realize that these APIs aren't free, these large organizations are earning by selling their data with other organizations. In the year 2020, people started to see Web3.0 as a solution to all the privacy concerns as it is based on Blockchain.

As the world is progressing, we are becoming more and more dependent on these APIs to make our lives comfortable. There is still a lot that we are yet to know about the limits of APIs. The future definitely has endless possibilities.
Now that the world has adopted APIs, upcoming is the era of Testing APIs. If you write APIs and are looking for a no-code tool you can check out my open-source project - Keploy.