1) The birth of the service oriented architecture as a standard at Amazon
2) Took place long before AWS was used by Amazon's commercial business, and most software systems were monolithic, requiring mainframe-like dedicated hardware.
3) Was inspired due to the epic spaghetti monster known as FC Software, whose entire non-architecture revolved around a massive Oracle database.
When Amazon hit the limits of scaling the Oracle databases with beefier hardware, they realized what a clusterfuck they had created. There were literally hundreds of applications, doing different things, but all connected to the oracle database. The oracle database functioned as a database, but also as a high throughput queue, as well as a message passing platform. At high loads, different applications were hitting the same rows so frequently that the transaction errors alone could bring down an entire fulfillment center.
And it should also be noted that it was the same FC Systems (the inspiration for the move towards SOA) that took 12 years to finally get rid of Oracle.
Moral of the story: you need competent software architects, and at the very least, a scalability plan. Also, fuck Oracle.