- DaCOokiEMon5TA3
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- Honorable Member
Humanity achieved an advanced state early in its history, achieving a high level of technological sophistication and expanding outward along the Orion Arm to escape Forerunner control thousands of years before the activation of the Halo Array. At one point, humanity formed an alliance with the San 'Shyuum and later warred against the nascent Flood. While humanity managed to drive the Flood off the galaxy for the next several millennia, the conflict led to a war with the Forerunners, a war which humanity lost. As punishment, the humans were stripped of their technology, their civilizations smashed, and the remnants exiled to their homeworld, reduced to a pre-technological state from which they would be forced to start again.
Borrowed from halo wiki
im guessing the war started because the humans didnt want to be controlled by the forerunners anymore or looking at the other comments it could be because the humans colonized on planets the forerunners didnt want them to because they wanted to escape from the flood.