In Peter F. Hamilton's Commonwealth Saga, the Primes invaded the Commonwealth with overwhelming numbers and force. On their first attack, they opened almost a thousand wormholes into Commonwealth space, and deployed tens of thousands of spaceships, each armed and defended to the teeth with nuclear and electromagnetic weaponry. The Commonwealth was massively underprepared. They only had miniscule municipal defenses on their planets, and only a few working starships. Even Earth was under-defended at the time. MorningLightMountain deployed far too many resources to too few planets. Each planet recieved thousands of starships, and each planet didn't have any defenses to ward those starships off. Each planet was conquered in a matter of hours. Nearly instantaneously. What kept MorningLightMountain from invading all of the Commonwealth planets simultaneously? Did it over-estimate human capability? If so, it did so massively. And how could it? It has Bose's thoughts. It should know just how weak humanity was.
The wormhole technology in the universe had a maximum range, which is why the Commonwealth had to create a starship to reach the Primes' star. This meant that the Prime's attack had to be done in stages building new staging posts for more wormholes to reach the inner parts of the Commonwealth.
MorningLightMountain's attack easily defeated the defences of the closest human star systems, although the SI being able to hack the communications to its motiles would have caused it to be more cautious before launching the next attack.
The Commonwealth, with the help of the SI, was able to come up with new technology and deploy it in an incredibly short time scale, so by the time the next phase of the attack started they were able turn the tide through superior technology, both the shielding technology and the quantum buster missiles.
MorningLightMountain's downfall was that it could not understand humans. It had the Bose memories as a reference, but quickly found Dudley's individual knowledge and skills largely unhelpful against Commonwealth tacticians. It never understood humanity or what they were capable of. When the quantum busters are first deployed, it couldn't understand why the weapons weren't used earlier. The concept that humans would have the means but not the inclination to kill it never occurred.