Exactly how much of the internet was impacted is unclear, but estimates typically put Microsoft Azure at around 20% of the global cloud market.
The firm said it believed the outage was a result of "an inadvertent configuration change".
In other words, a behind-the-scenes system was changed, with unintended consequences.
The concentration of cloud services into Microsoft, Amazon and Google means an outage like this "can cripple hundreds, if not thousands of applications and systems," said Dr Saqib Kakvi, from Royal Holloway University.
"Due to cost of hosting web content, economic forces lead to consolidation of resources into a few very large players, but it is effectively putting all our eggs in one of three baskets."
Recent outages have laid bare the fragility of the modern-day internet, according to engineering professor Gregory Falco of Cornell University.
"When we think of Azure or AWS, we think of a monolithic piece of technology infrastructure but the reality is that it's thousands if not tens of thousands of little pieces of a puzzle that are all interwoven together," said Mr Falco.
He noted that some of those pieces are managed by the companies themselves while others are overseen by third parties such as CrowdStrike, which last year deployed a software update that affected more than eight million computers run on Microsoft systems.
