The Fall Of Persia IX

The Fall Of Persia IX was what sparked the short-lived Human-Banished war, and killed thousands.

Beginning
After a large CCS-class carrier came out of slipspace, many on Persia IX panicked and prepared for a war, which they would receive. The ship turned out to belong to the Banished, and in a show of force, sent four phantoms down to the planet, being aided by multiple Scarabs as well. Many were killed by the attack and the UNSC forces on the planet began fighting back. Unfortunately, Persia IX didn't spent too much time expanding the UNSC troops in the area, and they were outnumbered.

The Battle Of New Dellend
The Banished quickly attacked the city of New Dellend, where there was much resistance from UNSC forces. It, however, led to the destruction of the city.

End
The Banished, now knowing that the Humans would fight back, made the decision to glass Persia IX in a show of force, and thousands were killed in the event.