Father heaven hated anything outside of normal so he bansihed all of his children execpt the titans to the underworld.
Titan Cronus was mad at his father for banning his siblings to the underworld and decided to kill him.
Cronus had kids and swallowed them becuase he found out that one of his children would dethrone someday. Cronus's wife had saved one of the children from being swollowed. This childs name was Zeus.
When Zeus became a adult he grew mad at his dad for what he had done to his siblings. Zeus fought Cronus and won. Partly becuase Zeus had his siblings spit up. Zeus started a war with hundered headed monsters. And won.