Why does Brutus decide to free the Trojans from the nonfiction book, The History of the Kings of Britain?

Brutus goes into exile following the accidental slaying of his father and finds himself in Greece. In Greece, Brutus learns that a large number of Trojans are being kept in captivity. Brutus stays with these people and soon becomes a leader well respected for his battle prowess, wisdom and generosity. Aided by a Greek man named Assaracus, Brutus assumes a leadership role and begins planning to undertake the freeing of the Trojan slaves.