The first battle of the Klingon War.
In the mid-2250s the Klingon Empire was fractured into rival houses, and a zealot named T'Kuvma sought to unite them against what he saw as a Federation threat to Klingon identity. He lit a beacon and gathered followers, and when the USS Shenzhou arrived to investigate, the situation was already on a razor's edge.
Commander Burnham urged a preemptive strike to show strength, but Captain Georgiou refused, and in the confusion Burnham committed mutiny trying to force the issue. When Starfleet ships arrived at the Binary Stars system, fighting broke out. Captain Georgiou was killed by T'Kuvma, and Burnham killed him in turn, which made T'Kuvma a martyr and deepened Klingon resolve. Admiral Anderson was also killed in the fighting.
The battle was the opening clash of the Federation-Klingon war. Burnham was court-martialed and imprisoned, setting her on the path that led her to the USS Discovery, while the Klingon houses stayed divided but angrier. Sarek, Cornwell and other leaders had to reckon with a war neither side could easily end.