The idea that the Covenant were defeated in 25𐦠⑴ is the central climax of the original Halo trilogy, marking the end of the 28-year Human-Covenant War, though formal peace treaties were finalised in early 2553. 

2552 was the deadliest and final year of the war, characterized by the fall of Reach, the invasion of Earth, the Great Schism, and the final battle at the Ark.

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Our Mistory

 

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Beyond the ordinary

 

Key Factors Leading to the Defeat (2552).

 

The Great Schism: The Prophet of Truth replaced the Sangheili (Elites) with the Jiralhanae (Brutes) as the primary military force, causing the Elite species to be ejected from the Covenant, leading to a massive civil war.

Alliance with Humanity: The Sangheili, led by the Arbiter (Thel 'Vadam), realized the Prophets were leading them to destruction and allied with the UNSC to defeat the Covenant Loyalists.

The Flood: The parasitic Flood outbreak on High Charity (the Covenant capital) and installation 05 broke the Covenant structure from within.

Final Battle at the Ark (Dec 11, 2552): Master Chief and the Arbiter successfully killed the Prophet of Truth and destroyed the Flood, ending the war. 

Post-2552 Reality:

Broken Empire: The Covenant ceased to exist as a unified entity, fracturing into smaller splinter factions.

Treaty of 2552: While hostilities ended in December 2552, the formal ceasefire between humanity and the Swords of Sanghelios was ratified in early 2553.

Survival: Humanity survived, but with over 23 billion casualties and the loss of the majority of their colonies.