Software integration has been a concern for several decades. It was first encountered in the 1980s and early 1990s. In those days, when batch processing was still the way many systems worked, common methods of integration were file transfers and remote procedure calls.
In the 1990s two different integration trends began emerging. One was the development of point-to-point and message queueing integration which supported more real-time needs. The other was software applications that combined many functions together and removed the issue of integration completely – this was the emergence of tightly integrated applications and the ERP industry.
By 2000, a new integration technology was introduced, the enterprise service bus (ESB). ESBs provided a centralized topology and offered more tools to manage integrations, and they could deal with early Internet-oriented integration protocols like SOAP. Also in 2000, a company called Salesforce was starting that only provided its software via the cloud and licensed it on a subscription basis.
As the Internet grew, cloud- and web-based applications became more mainstream, and the development of APIs arose as the solution to the integration challenge. The advantage of APIs is that they enable more loosely-coupled applications to work together, this in turn has created the opportunity for businesses to adopt more specialized applications and cloud-based systems.