As Yegge’s recalls that one day Jeff Bezos issued a mandate, sometime back around 2002 (give or take a year):

• All teams will henceforth expose their data and functionality through service interfaces.
• Teams must communicate with each other through these interfaces.
• There will be no other form of inter-process communication allowed: no direct linking, no direct reads of another team’s data store, no shared-memory model, no back-doors whatsoever. The only communication allowed is via service interface calls over the network.
• It doesn’t matter what technology they use.
• All service interfaces, without exception, must be designed from the ground up to be externalizable. That is to say, the team must plan and design to be able to expose the interface to developers in the outside world. No exceptions.

The mandate closed with:

Anyone who doesn’t do this will be fired.  Thank you; have a nice day!

.. If you were human resources and you needed some numbers from marketing, you had to get them using an API.  He was asking every team to decouple, define what resources they had, and make them available through an API.

.. Yegge’s  points out that, “Organizing into services taught teams not to trust each other in most of the same ways they’re not supposed to trust external developers.”