Final answer:
King Minos went to war on Athens due to the assassination of his son by an Athenian, which is part of the story involving Theseus and the Minotaur from Greek mythology.
Step-by-step explanation:
The event that caused King Minos to go to war on Athens in the tale of The Cruel Tribute was (a) The assassination of King Minos's son by an Athenian. This is a story from Greek mythology associated with the legend of the Minotaur, where Athens was forced to send tributes of young men and women to be sacrificed to the creature that lived in the Labyrinth of Crete, as a result of the death of King Minos's son at the hands of Athenians. Theseus, the Athenian hero, later volunteers to be part of this tribute with the intention of slaying the Minotaur and ending the cruel practice.