75 children are abducted and conscripted into the UNSC's Spartan II program. John is among them, and becomes squad leader shortly after training begins.
2525: THE HUMAN / COVENANT WAR BEGINS
The Human/Covenant War begins. Though it won't be revealed for many years, the Covenant attacked Humanity only after learning that Humans, not the Prophets were the Forerunners' favoured race.
The fourteen year-old Spartan IIs undergo extensive cybernetic and genetic modification. Thirty die, twelve are disabled.
The Spartans, equipped with Mjolnir Mk IV armour engage the Covenant above Chi Ceti IV, boarding and destroying a Covenant capital ship with the loss of only one man.
2531: HALO WARS
Troops from the UNSC Spirit of Fire engage Covenant troops of the partially-glassed planets Harvest and colony world Arcadia.
A gateway opened from Arcadia leads the Spirit of Fire to an isolated Forerunner Shield World where Humanity makes first contact with the Flood.
Sergeant John Forge detonates the Spirit of Fire's slipspace drive and destroys the planet. The Spirit of Fire's crew escapes and begins its long journey home in cryosleep. As of 2553, it has not made it back.
2532: SPARTAN III
The first 300 volunteer Spartan IIIs enter training. Cheaper and weaker than Spartan IIs, the IIIs are to be produced in much greater numbers with far fewer casualties.
Desperate for a propaganda victory, the UNSC makes the Spartan II program public. Spartan IIs become legendary. When killed, they are listed as Missing in Action to maintain the image of their invincibility.
2552: HALO REACH
While Earth still eludes them, The Covenant find Humanity's second home of Reach.
August 14 Noble Team takes down a Covenant Supercarrier. It is immediately replaced by hundreds more.
August 23 Noble Team helps evacuate city of New Alexandria. The city is glassed.
August 30 Noble 6, Emile-A239 and Carter-A259 die evacuating Cortana's AI core to the UNSC Pillar of Autumn. Then the Pillar of Autumn makes a slipspace jump using secret Forerunner data entrusted to Cortana.
September 19-22 The Forerunner data leads the Pillar of Autumn to Halo 04. John 117 is awoken from cryosleep and tasked with protecting Cortana and the location of Earth. The Pillar of Autumn crash lands.
John 117 makes contact with the Flood imprisoned in Halo 04's research centres. Halo's Monitor, 343 Guilty Spark, attempts to use John to activate the Halo array. Cortana prevents the activation and John detonates the crashed Pillar of Autumn's engines, destroying Installation 04.
In Halo: Anniversary, 343 Guilty Spark suggests the destruction of the Halo will awaken and anger the Didact.
2552: HALO 2 & HALO ODST
October 20 John 117 arrives on Cairo Station and is equipped with Mjolnir Mk VI armour.
Searching for the Ark, the Covenant accidentally discover the location of Earth. John returns home but quickly follows the Covenant's High Prophet of Regret's retreat back to Halo 05.
Earth is assaulted by Covenant forces searching for the Ark. An ODST squad in the city of New Mombasa engages in a series of skirmishes with Covenant ground forces.
November 2 John 117 arrives in Halo 05, assassinates the Prophet of Regret, and encounters the Flood Gravemind.
The revelation of the Halo array's true purpose creates a schism in the Covenant, turning the doubting Elites against the true believers from the Prophet-controlled races. The Gravemind uses it as an opportunity to seize the Covenant capital.
John 117 returns to Earth.
2552: HALO 3
November 17 John 117 ejects from the Covenant-controlled Forerunner Dreadnought and falls to Earth. The Forerunner artefact buried under the ocean near Voi is activated by the Covenant, opening a portal to the Ark.
December 11 Human and Elite ships arrive above the Ark and engage Covenant forces attempting to activate the Halo array.
John 117 and the Arbiter activate the replacement Halo 04 and escape through the Voi portal aboard the UNSC frigate Forward Unto Dawn. Halo 04's activation wipes out the Covenant forces, the Flood, and the Gravemind.
The activation closes the portal mid-transit. The Arbiter returns to Earth on December 23. John 117 is lost in space and enters cryosleep.
The Elites seize control of the Covenant. The Human/Covenant war ends.