The Battle for Earth was a large-scale space, air, and ground battle between the invading Covenant forces and the UNSC Home Fleet on and around Earth at the end of 2552. The entire battle spanned over two months, and events that took place during the conflict spawned several simultaneous battles, including the Battle of Installation 05 and the Battle of Installation 00.
The initial attack was initiated on October 20th, 2552 by the Fleet of Sacred Consecration and the Prophet of Regret, who was led to the planet by a Forerunner Luminary that told him of a portal that existed on Earth. Upon arrival, the fleet realized they had entered the home system of humanity, and with only a fifteen-ship fleet, were not prepared for a full-scale battle. Due to the presence of humans, the Prophet of Regret was forced to flee to Installation 05, which spawned a battle between Covenant and UNSC forces on Delta Halo.
Around the same time, the Prophet of Truth initiated his purge of all Sangheili from command roles, and sent the Fleet of Furious Redemption, a fleet led by Jiralhanae, to take control of the invasion of Earth and complete the destruction of the planet. Within a month, most of Earth's defenses were eliminated.
In addition to attacking human forces, a significant contingent of Covenant were sent to Voi, Kenya to excise the Forerunner portal that the Prophet of Regret had come to find in the first place. By the middle of November, the portal was almost completely excavated.
The Prophet of Truth arrived on November 17th, 2552 via the Forerunner Dreadnought, and immediately headed to the portal. Upon activation, most of the Covenant fleet followed the Prophet of Truth into the portal and to the Ark to attempt a firing of the Halo Array. Only a single UNSC ship followed them. This began the Battle of Installation 00.
Earth was granted a significant reprieve with the disappearance of most of the invading ships, and began to destroy and remove the remaining Covenant forces. A Flood-infected battlecruiser arrived almost as soon as the Covenant fleet left through the portal, and a large area of Africa was glassed to contain the outbreak. With only a handful of Covenant forces remaining on the planet, the UNSC was able to neutralize the remaining threat and declare a victory.
These events are depicted in the video games Halo 2, which was the subject of several Mission Debrief episodes in fall to winter 2018, Halo 3, which was the subject of several Mission Debrief episodes in spring to summer 2019, Halo 3: ODST, which was the subject of several Mission Debrief episodes in winter to spring 2019, the short story Palace Hotel from the anthology Halo: Evolutions, and the comics Halo: Uprising and the Halo Graphic Novel.