Human-Covenant war

United Nations Space Command
Leaders: HIGHCOM

Homeworld: Earth

Military Forces: Exact numbers are unknown.

The Covenant
Leaders: The High Council

Homeworld: High Charity

Military Forces: Exact numbers are unknown.

2525

 * The UNSC makes first contact with the Covenant at the UNSC colony world Harvest. The Covenant destroy the colony without warning or provocation.
 * Spartan IIs help win the very minor Battle of Chi Ceti.

2530

 * The Covenant destroys the UNSC colony world of Eridanus II.

2531

 * Battle of Harvest. The UNSC and Covenant meet in ship-to-ship combat for the first time; the Covenant are outnumbered and outgunned, nevertheless the battle is a close victory for the Humans.

2535

 * The Covenant destroys the UNSC colony world of Jericho VII in the Battle of Jericho VII.
 * In the course of four short years, UNSC forces have been hammered, despite excellent leadership and tactical brilliance. It is simply a matter of being outgunned; Covenant kill ratios tend to top three to one in ship-to-ship combat. By 2535, virtually all of the Outer Colony worlds have been destroyed by the Covenant.

2536

 * Covenant forces begin to swarm into the Inner Colonies. For several years the war falls into a pattern: humans win isolated battles, typically during ground operations, but at a horrible cost. In space combat, the humans are losing at a precipitous rate, and one by one, the colonies fall.

2537

 * The Battle of New Harmony
 * The Battle of New Constantinople
 * The Siege of the Atlas Moons
 * Operation: PROMETHEUS: Spartan-III Alpha Company is killed by Covenant forces

2544

 * The Battle of Miridem

2545

 * Operation: TORPEDO: Spartan-III Beta Company is killed by Covenant forces

2549

 * The Siege of Paris IV

July
August:
 * Battle of Sigma Octanus IV in the Sigma Octanus System. It is the UNSC's single greatest victory since Harvest. The Covenant, however, gain what they are looking for: the location of Installation 04. They also determine the location of Reach.
 * Battle of Reach. In the largest naval battle yet in the war, 314 Covenant ships destroy 152 UNSC ships and 20 MAC gun platforms around Reach, and win a major victory, destroying the UNSC's last great military stronghold, besides Earth.

September

 * The Battle of Installation 04. A single UNSC ship, the UNSC Pillar of Autumn escapes to Installation 04. After four days of hard fighting, the Covenant discover the Flood organism and Forerunner constructs, hampering their efforts to control the installation. The melee ends with Installation 04 destroyed with only a handful of survivors.
 * Operation: FIRST STRIKE. Six SPARTAN-II supersoldiers are able to rout and destroy a fleet of 500 Covenant starships preparing to jump to Earth.

October

 * The First Battle of Earth. Though a relatively small and lopsided battle; 15 Covenant ships fighting 75 UNSC vessels and 300 MAC platforms, the event is significant in that the Covenant discover the location of Earth. The UNSC wins the fight.
 * The Battle of Installation 05. A single Covenant ship survives the battle of Earth and retreats to Installation 05. It is pursued by a single UNSC ship, the UNSC In Amber Clad. Again, a massive fight ensues between the UNSC, Covenant, Flood, and Forerunner Constructs. The Flood appear to win control of the Installation.
 * The Civil War of the Covenant begins. Covenant forces are thoroughly divided between the Elites and the Brutes. Every race in the Covenant takes sides.
 * The Second Battle of Earth. The Brute faction of the Covenant returns to Earth in force, apparently conquering Africa.

November

 * The Battle of Onyx. The destruction of Installation 04 trigged Onyx sentinels to appear. The covenant followed the covenant destroyer that a SPARTAN-II team called blue team took to onyx. The battle ends in the same way of the Battle of Installation 04.
 * Civil War of the Covenant- The battle continued.
 * The Second Battle of Earth- The battle continued.