Pact of the Big Three

The Promise is a deal made by the Big Three gods, Zeus, Poseidon, and Hades, after World War II. Because the war was started by powerful demigods, they vowed to have no more children. Zeus was the first to break the Promise, giving birth to Thalia. Next to break the promise was Poseidon, who fathered Percy Jackson. Although Hades did not technically break the Promise, two of his children, Bianca de Angelo and Nico de Angelo, spent time in the Lotus Hotel. They came out after World War II, although they were born before it. In all, there are four demigods who are sons or daughters of the Big Three, although Bianca is believed dead.