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. 

Spartan-III Alpha company was the first of three Spartan-III companies to be recruited, trained, and put into service.

Spartan-III Beta company was the second of three Spartan-III companies to be recruited, trained, and put into service.

Spartan-III Gamma Company was the last of three Spartan-III companies to be recruited, trained, and put into service.

Operation: RED FLAG was a planned operation by both the Office of Naval Intelligence and the UNSC to use Spartans to capture a Covenant ship, use it to penetrate into Covenant space, and capture a Hierarch, with the intent of using the Prophet to broker a cease-fire.

The Siege at Kolaar was an attack on Arbiter Thel 'Vadam and his forces by Avu Med 'Telcam and the Servants of the Abiding Truth in the first major conflict of the Sangheili civil war.