From Halopedia, the Halo wiki
Discuss the general timeline and sequence of events
Talk about UNSC military buildup in the outer colonies here, alongside insurrection and spartan 2
Discuss the Covenant expansionsim leading them into the human sphere
First contact and declaration of war
Discuss the first battle of harvest here, alongside the Covenant declaration of war on humanity
Course of the war
Retaking Harvest and the Harvest campaign (2526-2531)
Discuss Cole's retaking of Harvest and the events of Halo Wars here
Outer Colonies Massacres (2525-2536)
Discuss the Outer Colonies theater here, including SILENT STORM, Mesra, Netherop, Circinius IV, Alpha Corvi II, Cole's campaigns in Halo Wars genesis, Etran Harbourage and any other action against the Covenant prior to 2536.
War on two fronts
Discuss the ongoing insurrectionist threat including SILENT STORM, Ghosts of Onyx, Gao and other actions taken against insurrectionist forces during the war.
Inner Colony Sieges (2536-2551)
Discuss the Inner Colonies theater during the latter half of the war.
Final year (2552)
Discuss the grim outlook during 2552, the fall of numerous crucial inner colonies and the Fall of Reach
Great Schism and fall of the Covenant (October-December 2552)
Discuss the events of the Halo Trilogy and the events leading to the war's end
Discuss the aftermath of the Covenant war here, the ongoing war between the elites/brutes, insurrectionist resurgence and so forth
Discuss the technological and etc advancements brought around by the war