Oedipus killed his father and married his mother, brewing a human tragedy. Oedipus's son, Polynices, waged a war against Thebes with seven rulers to battle for power with his brother, resulting in fratricide, as both died under the city of Thebes.
This was the consequence of marrying a goddess, and it was only the beginning. On another timeline, the Trojan War erupted afterward.
When the great war began, Thebes, under Greek influence, should have sided with Greece to secure victory. However, the king of Thebes at that time, Eteocles, had a daughter named Andromache, who was married to Prince Hector of Troy...
Thus, later, the powerful mortal demigod, hero Achilles, ranked almost second to Heracles, led forces to massacre Thebes, killing Andromache's seven brothers in one day.
Greek mythology nearly concluded here, but no one knew whether the disaster of Thebes ended as well.