Human-Covenant war

OVERVIEW

A battle takes place between the UNSC and the Covenant

TIME LINE OF THE CONFLICT

• Feb 03. 2525 - Contact with the peaceful outer colony of Harvest is lost after reporting contact with a unknown ship. A small scout ship, the argo is sent to investigate. 
• Apr 20. 2525 - The argo arrives on station and makes a brief report, the ship is never heard from again.
• Oct 07. 2525  - A UNSC battle group consisting of two frigates and one destroyer is sent to Harvest. There they discover that the surface is glassed and discover one ship orbiting over the colony.  The ship proceeds to attack the battle group and destroys both the frigates and badly damages the destroyer.
• Nov 01. 2525 - Vice Admiral Preston Cole begins to mobilize the largest UNSC fleet in history to retake Harvest
•  IN          2531 - Cole's fleet retakes Harvest but at a tremendous cost; 2/3rds of his fleet is destroyed
•  IN          2532 - Events of Halo wars take place
•  IN         2535 - The Cole protocol or United Nations Space Command Emergency Priority Order 098831A-1 is initiated. This order bars any ship from traveling straight to any of the inner colonies as it could inadvertently give away their position. As such, ships must generate randomized exit vectors.
•  IN          2536 - After wiping out almost all of the outer colonies, the covenant start attacking inner colonies, the UNSC almost never wins in Space and morale is beginning to run dangerously low
• 2536 - 2552 - Covenant keep pushing into the inner colonies and even with the help of the Spartans the tide of the battle cannot be reversed.
• Jul 17. 2552 - The human colony of Sigma Octanus comes under attack and Commander. Jacob keyes successfully defends the colony against overwhelming odds. He is promoted to Captain.
• Aug 25.2552 - The Pillar of Autumn is chosen for a special mission by Dr. Catherine Halsey and Jacob keyes is chosen to captain her. Assisting him in the mission is Cortana and Master Chief.
• Aug 30.2552 - Before the autumn can begin its top secret mission, Reach is attacked and every ship in a three system vicinity is told to drop what its doing and help defend Reach. Majority of the   Spartans go ground side to help defend the planet and are believed to be lost when the Covenant glass the planet. The fleet over Reach is obliterated and the MC escapes aboard the pillar of autumn and is believed to the last remaining Spartan. The events of Halo take place afterward.
• Sep 04.2552 - Lt.Wagner reports to the high command on Earth and formally informs them off Reach's destruction. He also informs them of the very real possibility that all Spartans are dead*
• Sep 07 2552 - On Reach, Dr. Halsey and a small number of Spartans are holed out underground. They discover an ancient cavern that among many things has a forerunner crystal. Dr.Halsey takes the Crystal and  Admiral whithcomb is also rescued by the Spartans on Reach.
• Sep 19.2552 - The pillar of autumn arrives at Alpha Halo and after putting up a fight is crash landed by Jacob keyes on halo's surface. A significant contingent of the on board marine force is killed trying to repel borders but the rest of the surviving ones escape to the planets surface and are under the command of ODST Major. Silva. Cortana and the Master chief also escape to the surface of the planet where they help in setting up a temporary base of operations. Captain keyes and several high ranking officers are captured by the Covenant and all of them with the exception of the captain are executed.
• Sep 20 - 21 - When the flood is discovered on Halo; the Covenant High command orders every ship in the vicinity of Halo to jump to slipspace and "abandon" the ring. This is done out of fear of the parasite possibly spreading to other areas of the galaxy. This move costs them dearly as they are not able to resupply their troops efficiently and quickly.
• Sep 22.2552 - The Master chief and Cortana escape aboard a Longsword fighter after rigging the reactor of the Pillar of autumn to explode thereby destroying the ring and the flood threat on it. Major Silva and his troops commandeer a flood infested Covenant ship and attempt to escape from the Surface of the planet but are killed when the ship crashes.
• Sep 23.2552 - The master chief along with Srgnt. Johnson, Lt. Haverson, Locklear and Polaski successfully board and take over a covenant flagship(The Ascendant justice) that had come to investigate the destruction of Halo, and they take it to Reach. 
• UNKNOWN/ SPACE-TIME ANOMALY - Chief returns to Reach and mounts a rescue; when in slip space the forerunner crystal is shown to have curious space/time manipulation powers. As such the date is actually closer to Sep.12 2552. After a battle in an altered state of slip space, the Ascendant justice is heavily damage and is taken to a Pirate colony for repairs. A few Spartans are killed when they try to repair the ship while in slip-space and this brings the total number of surviving Spartans to single digits. Dr. Halsey drugs Kelly and escapes with her on a shuttle and before she leaves, Dr. Halsey gives the forerunner crystal to Locklear with orders to destroy it; which he does(He is killed by the radiation from the subsequent blast)
• UNKNOWN/ SPACE-TIME ANOMALY- Cortana discovers the Covenants plan to invade Earth with a massive fleet  of about 500 ships and discovers that their rally point is at a command and control station called Unyielding Hierophant.  Master chief and the surviving Spartans infiltrate the facility and set the Cores to detonate. Admiral Whitcomb and Lt. Haverson aboard the crippled Ascendant justice ploy the covenant forces to follow them close to the station which explodes killing them as well as the majority of the covenant fleet. John, Linda, Will, and Fred; the last known remaining Spartans, along with Sgt. Johnson and Cortana depart for Earth to warn them of the Covenant's discovery.

• Oct 20.2552 - MC, Johnson and Keyes(posthumously) are decorated, the previous supreme commander of the fleet of particular justice, the one responsible for safeguarding Halo is branded a heretic and punished. The first battle of Earth takes place and the Chief goes ground side to New mombasa to repel the Covenant there and then returns to In amber clad and follows the Prophet of Regret when the escapes to Delta halo. Once there the events of Halo 2 take place.
• Nov 03.2552 - Dr.Halsey along with Kelly arrive on Onyx and are attacked by the sentinels there, once on the ground they team up with Kurt and the Spartan-III's. She also puts in a request to have all the Spartans meet her at Onyx. Fred, Will, and Linda are dispatched to Onyx and to speed up their journey they hijack a Covenant Cruiser. The Covenant become aware of the ship and its final destination. Plans are drawn up by the Separatists to go to Onyx to reclaim lost Forerunner technology.[ *Note* - Humans and Covenant are not allies yet, even though Johnson and the Arbiter worked together during Halo 2.] The shield world is turned on and the remaining Spartans along with Halsey are pulled into the "void". The contingent of Elites that had landed on the planet and attacked the Spartans were all killed when Kurt sacrificed himself to activate a nuclear warhead thereby destroying everyone. Will is also killed.
• 2552 - 2553 - The events of Halo 3 take place. Second war of Earth begins and the portal on Earth is activated leading to the ark. Miranda keyes is killed by Truth and then Srgnt. Johnson is killed by 343 Guilty spark when he tries to activate the replacement ring. The brute fleets are destroyed by the Elites and the prophet of Truth is killed by the Arbiters hands thereby dismantling the Covenant loyalists.The ark is destroyed when the replacement ring goes off and takes with it the gravemind and all the flood that were on the surface. The Arbiter escapes through the portal to Earth but the Chief's part of the ship(the Rear) is sheared off and is seen floating in space at the end of Halo 3.
• Mar 03.2553 - The Human-Covenant war ends and a memorial is built in remembrance of the victims, the chief is thought to be dead but following the notion that Spartans never die, he is declared as MIA as are the rest of the Spartans.

A large scale battle that is taking place in Halo wars that is set during the harvest wars

Master chief entering a room in Halo: CE

Regret's carrier above New Mombasa in Halo 2

The chief looks on as the Portal is activated over the skies of New Mombasa in Halo 3