2500 (MMD) was a century common year starting on a Friday and the 2,500th year of the Common Era (CE). It was the 500th year of the third millennium and last year of the 25th century. This rendering is concordant with the United Nations Space Command's military calendar. The year 2500 took place during the Covenant's 23rd Age of Doubt. It saw a major change in the UNSC's tactics used against the Insurrection, as Operation: KALEIDOSCOPE was launched this year. The Outer Colony, Meridian, was also retaken in 2500.
- March 9: Preston Cole sends a communiqué to his wife, Inna Volkov, urging her to reconsider her recent filing for divorce.
- Fall 2500: Captain James Cutter was sent to the UNSC School of the North Star, on Earth, to study astro-navigation and political science.
- The UNSC initiates Operation: KALEIDOSCOPE, a series of highly classified surgical strikes against prominent insurrectionist leaders.
- The UNSC wrests control of Meridian from the Sundered Legion during the Siege of Athea.
- Carlos Wambua is born.