On the 3rd of February, 2525, the human colony of Harvest was attacked and decisively decimated by the alien union known as the Covenant Empire. For the next 26 years, Humanity and the Covenant Empire would wage war, with the Covenant making rapid progress towards the homeworld of humanity. By far they were the greatest threat to humanity in the known galaxy.
Admiral Preston Cole proved the only major naval threat to the Covenant, achieving numerous ‘victories’ from 2525 until his disappearance in 2543. The Second Battle of Harvest, the Battle of Alpha Aurigae, the Battle of Xi Boötis A, the Battle of great Bear, and the Battle of Psi Serpentis, all moments that made Admiral Preston Cole a household name, and a hero of the war. And yet, all were in many ways pyrrhic victories, with huge numbers of human vessels being destroyed and, in one instance, two whole colonies. The Battle of Psi Serpentis saw two Covenant fleets wiped out, for the cost of Admiral Cole himself.
One of the greatest heroes of the war, and almost all of his major victories came at great cost. Truly, the Covenant was an unstoppable enemy.
Even when the Covenant lost, they did innumerable damage, killing thousands to millions of humans in the process, leaving planets scorched, and decimating whatever human fleets were in the area, making them far too weak to take on the next enemy, which was always an inevitability. No one would go through the war fighting the Covenant once.
The SPARTAN-II Program, headed by Doctor Catherine Halsey, was perhaps one of the few reasons the war took so long, and gave humanity the chance it had to survive. Though countless humans, members of ONI, the UNSC, and even the Program itself, felt that the S-II Program was a cruel and unusual thing, countless others agree that without it, humanity would be long lost by now. Kurt-051 and John-117 each caused more damage to the Covenant than some whole human fleets, and countless other SPARTAN-IIs all across the war saved countless lives. The later SPARTAN-III Program proved almost equally as important, taking out key manufactories and Covenant forces, though at greater costs than the SPARTAN-IIs.
Even in spite of this, the companies of SPARTAN-IIIs were almost always wiped out, and there were so few SPARTAN-IIs even in the beginning of the war. Such small numbers can hardly change the tide of conflict.
Indeed, by 2552, the human governments and agencies were sure all was lost. The last thing they could do was hold out and hope for a miracle.
In the year 2551, nothing occurred between both sides.
In 2552, humanity won the war.
What is it that caused this drastic turn of events? Well, in 2552, many things happened that could have caused such a thing. The Fall of Reach saw 300+ to 750+ Covenant ships attacking the planet. One would expect 750+ Covenant ships to be able to level the planet quite easily, even with the vast defences employed by the UNSC. However, this battle turned into a pyrrhic victory for the Covenant, despite the destruction of Reach, the obliteration of a massive numbers of UNSC ships, millions of human deaths, and the almost complete destruction of the SPARTAN-IIs.
Not long after, the Battle of Installation 04 occurred. Here, it could be said, the whole fate of the war changed, as the installation which was regarded as a holy artefact by the Covenant Empire was destroyed by a SPARTAN-II, and the Supreme Commander Thel 'Vademee was demoted and branded a heretic for his failure in defending the ring. It was here, perhaps, that the Covenant began to splinter, as the already present Covenant Heretics had fled the Halo ring, with knowledge of what it was. Thel 'Vademee proceeded to eliminate them in hopes of gaining his honour back, but in the end he too was made aware of what the ring was. The Sangheili ware deemed heretics, and the Covenant was split in two. Surely, this was the turning point for the Covenant.
However, long before this occurred, that same SPARTAN-II, with the aid of a few other survivors, lead a raid on the Covenant facility Unyielding Heirophant. Despite losses, the facility was destroyed, along with nearly 500 Covenant ships - a fleet with one purpose; to stop anyone in their path.
A fort planet was destroyed, a massive fleet was destroyed, and the Empire was fractured. Surely this explains its new weakness.
Yet, it does not, for prior to any of these events, the Covenant and UNSC took part in at least five separate battles.
The Battle of Gamma Pavonis VII, a small engagement won due to the commanders own recklessness. Hardly a thing worthy of note.
The Battle of Ballast, a little known engagement. However, at the time of the Battle of Earth, ONI promoted that it had been a UNSC victory. Of course, it’s not as if ONI is known for being honest.
The Battle of Ariel, a land engagement between a large number of Covenant ground forces, and a single squad of ODSTs. It is not as if ODSTs have not had their fair share of input during the war, but their victory here makes it seem that the Sangheili, at the least, had become extremely less effective than was previously believed. Their influence over Kig-Yar and Unggoy is also noted, with numerous Unggoy retreating despite the commands of their leaders.
The Battle of Fumriole - much like Ballast, very little is known of this battle, but unlike Ballast, there is no known ONI propaganda of it. It was, however, likely to be a human victory, given the pattern.
And finally, the Battle of Sigma Octanus IV. While both sides claimed victory to this battle, it is notable due to the UNSC managing to successfully repel the Covenant force, which was near double it’s own size.
Prior to any major turning points or losses, the Covenant lost every known battle that occurred in 2552 before the Fall of Reach.
What is it, then, that made the Covenant so notably ineffective in 2552?
Well, of what we know of the Covenant, as the war went on the High Prophet of Truth was eagerly trying to replace the Sangheili with Jiralhanae. Even before the war occurred, it had been Tartarus sent to negotiate with the humans, not any upstanding Sangheili official or councillor. It is also said that the Unggoy had become even more poorly treated by 2552 than normal ( for example, it is mentioned in one instance that Unggoy were killed just to set examples onboard every Covenant ship, however the truth behind this is questionable and no date is given). So, one could perhaps theorise that in 2551, the Covenant had undergone many small problems and shifts, and perhaps even another Unggoy Disobedience.
T’vaoan, a sub-species of Kig-Yar, have made no known appearances prior to the Fall of Reach. One could then theorise that the Covenant had decided to make the T’vaoan their own separate military presence, rather than the simple Kig-Yar that were so well known by the UNSC and UEG. With this news, the Unggoy would surely have been sore, and perhaps attacked Kig-Yar and T’vaoan any chance they got, to the point of it being considered a disobedience.
The same could be said of the Mgalekgolo, who during the Battle of Earth saw two variants used actively, one in their blue armour and one in fitted gold armour, with a new form of assault cannon.
A 3000 year old Empire that had destroyed dozens of colonies, suddenly equalled and even bested by their 20+ year enemy. There must be more to it than simple chance.