Original: He was indicted as a major war criminal at the Nuremberg Trials on three counts: (1) conspiracy to commit crimes against peace, war crimes, and crimes against humanity; (2) Planning, initiating and waging wars of aggression; and (3) crimes against the laws of war.
Simplified: After the war Dönitz was charged and convicted of "crimes against peace" and "war crimes" at the Nuremberg Trials.