Earth
From Halopedia, the Halo wiki
Summary
Earth is the homeworld of the human race. It is the UNSC's last strong bastion of power, since Reach fell, and is heavily protected with Super MAC orbital platforms, over a hundred heavy cruisers, and many other experimental defense systems. The UNSC have taken no chances with keeping the secret of Earth safe, though it was only a matter of time before the Covenant discovered Earth's location.
Earth is the location of the Forerunner artifact, the Ark, and is probably the reason the Covenant came to Earth.
The Attack
In 2552, Earth came under attack by a fleet under the command of the High Prophet of Regret. It is likely that Regret came in search of a Forerunner installation (probably The Ark), possibly from directions from the Forerunner installation on Coral. Regret had never intended to face such a strong human force, and went after the installation himself while his fleet engaged the humans in orbit. His fleet included only 13 CCS-Class cruisers and 2 Assault Carriers.
For full details about the attack, see The First Battle of Earth.
That attack was repelled easily, however the humans had a far greater difficulty the second time around, when the High Prophet of Truth sent more Covenant forces to Earth, this time with the intent to capture the Forerunner artifact and activate the Halos, bringing an end to all life in the galaxy.
For known details about the attack, see The Second Battle of Earth.
