The Spartan II program, led by Dr. Catherine Halsey, was a plan by the Office of Naval Intelligence to use children with superior genetic traits to create a group of super-soldiers in order to put an end to the ongoing Insurrection in the outer colonies. 

The Battle of Chi Ceti was a battle between the UNSC Commonwealth and the Covenant vessel Unrelenting in the Chi Ceti system on November 27th, 2525.

The Battle of Alpha Corvi II was a battle between the UNSC and the Covenant forces in the Alpha Corvi system on December 3rd, 2525.

The Battle of Miridem was an engagement between human and Covenant forces on and around the colony of Miridem.

Operation: WARM BLANKET was an operation to recover Doctor Halsey from the Covenant after her capture during the Battle of Miridem in 2544.

The Fall of Reach was possibly the largest battle during the Human-Covenant War, taking place in the Epsilon Eridani system, in orbit and on the ground of Reach, humanity's largest military stronghold.

The Onyx Conflict was a major engagement between UNSC, Covenant, and Forerunner forces on and around the planet of Onyx in the Zeta Doradus system in October and November 2552.

The Requiem Campaign was a UNSC mission to return to Requiem, and take control of the shield world away from Jul 'Mdama and his Covenant remnants in February 2558, six months after the Battle of Requiem.

The Battle of Oban was a conflict between the UNSC and Covenant forces under command of Jul 'Mdama on the colony world of Oban in July 2558.

The Battle of Aktis IV was a conflict between the UNSC forces aboard the Infinity and the Covenant forces under command of Jul 'Mdama on the planet of Aktis IV in July 2558.

Operation: ATHENA was a covert UNSC mission to infiltrate the Song of Retribution, and retrieve the Janus Key from Jul 'Mdama and his Covenant remnant forces in September 2558.