The Battle Of Xahea was a major engagement between the Federation Starfleet and a fleet of Section 31 ships commandeered by Control in 2257. The battle was fought in the vicinity of Xahea. (DIS: "Such Sweet Sorrow", "Such Sweet Sorrow, Part 2")
In 2257, the USS Discovery stumbled upon a Sphere. However, the complexity of its communication and the breadth of its knowledge overloaded Discovery's systems, causing widespread malfunctions that the crew misinterpreted as the effects of a computer virus. Eventually, Commander Saru realized that a repeating pattern of ultraviolet lights being produced by the "virus" were linguistic in nature, and surmised the sphere's intent.
At Saru's urging, Captain Christopher Pike had the Discovery drop shields and allow the sphere full access, enabling it to complete the transmission and translation of its experiences. Meanwhile, the sphere's internal temperature rose from under 10,000 to over 10.036 Kelvin, a sign of its impending core collapse. A nanosecond before its death, the sphere reversed the polarity of its stasis field to push Discovery clear of its detonation. Its last sensor observation was of Spock's shuttle. (DIS: "An Obol for Charon")
While in orbit of Kaminar, Lieutenant commander Airiam was corrupted by an unknown force from the 28th century, which forced her to transfer all the information the sphere had gathered on artificial intelligence to Control, which later betrayed Starfleet and massacred the crew of Section 31 Headquarters by shutting off life support, though it was able to hide this fact by creating holograms of Admiral Patar and other Section 31 leaders and using them to communicate with Section 31 and Starfleet. (DIS: "Light and Shadows", "Project Daedalus")
While reviewing her mother's mission logs, Michael Burnham learned that her mother was responsible for placing the Sphere in Discovery's path. This was after she'd tried to destroy it to keep its data away from Control, which took over Leland. (DIS: "Perpetual Infinity")
Discovery continued to investigate the red bursts while keeping ahead of Leland/Control, and detected a fourth signal orbiting the Klingon world of Boreth. There, they obtained a time crystal, and began work to create a Daedalus suit of their own in order to take the Sphere data to the future, beyond Control's reach. However, they were surrounded by Section 31's fleet, now fully under Control's domination. Pike summoned the Enterprise to take on Discovery's crew before setting the ship to auto-destruct, in an effort to prevent Control from obtaining the Sphere data. Pike was left with no other option but to set the Discovery's auto-destruct system and call the Enterprise for immediate evacuation of the ship's crew. (DIS: "Through the Valley of Shadows")
However, they discovered that the Sphere data would also not allow the ship to be destroyed, leading to a change of plans - to bring Discovery itself into the future, and the data with it. After the decision was made to destroy Discovery to prevent its capture by Control, the ship deployed evacuation corridors to transfer its crew to Enterprise. Discovery had been unable to delete the Sphere's data from its computers, and had failed to destroy the data by auto-destructing the ship. A new plan was emerging: to create a new Red Angel suit, to be powered by the crystal from Boreth, charged with the help of Po, and use it to send Discovery itself on a one-way trip to the future, thus keeping the Sphere data out of reach of Control. Pike and other essential personnel returned to the ship to investigate a fifth red burst on the planet Xahea, where they welcomed aboard its queen, Me Hani Ika Hali Ka Po, who had developed a dilithium incubator that could be used to charge the time crystal. Discovery began retrofitting its fleet of shuttles and landing pods with enhanced weaponry, joined together with similarly-modified craft from the Enterprise, to combat the Section 31 fleet. At the same time, work continued on preparing the Daedalus suit, which would be worn by Burnham, as her mother's DNA was encoded into the suit schematics and she was the closest match. However, it was revealed that it would be a one-way trip, as the energy needed to charge the crystal with Po's incubator would make it unstable. The senior staff all chose to remain with Discovery and make the trip with Burnham. Pike relinquished command of Discovery back to Saru for the journey, and returned to the Enterprise to prepare for the battle to come. (DIS: "Such Sweet Sorrow")
Michael Burnham donned the new suit, and with the help of Spock realized that she needed to travel back to set five bursts in order to close the time loop: at the Hiawatha, Terralysium, Kaminar, Boreth, and Xahea. After she had done so, she created a sixth burst, aimed at helping Discovery cross through the wormhole created by the suit. She and Spock also agreed that she would create a seventh burst if the ship safely made it to the future. That burst was later observed.
Following the battle, Pike, his first officer Una, Spock, and acting Section 31 chief Tyler all reported to Starfleet Command that the Discovery was destroyed with all hands. Spock furthermore recommended that in order to prevent such incidents with Section 31 from happening again, that all participants in the event were to be barred from talking about Discovery, her crew, or her spore drive under penalty of treason. (DIS: "Such Sweet Sorrow, Part 2")