What deal does Hades make with the gods regarding Persephone?

Answer 1

Persephone was the daughter of the Godess of the seasons. Now before, there was 1 season all the time Summer.

But one day Hades saw Persephone and thought she was beautiful; so he kidnapped her and took her to the underworld.

Even then, she would not accept his offer to marry him so she stayed in the underworld for a few weeks, until her mother came looking for her. The Mother talked to Hades and as Her and her daughter were leaving, a soul ran up to Hades, and told him he caught her eating a Pomergranite.

She expressed that it was only the seed, and she had been so hungry. Hades apologized but said it still counted. Hades and her mother struck a deal to only have her spend half the year with him in the underworld IF she married him. (Fall and Winter)

Her mother (The Goddess of Seasons) is what causes the seasons. During the spring/summer, while Persophone is with her, She is happy and it's warm and everything is alive. But in the fall/Winter, while Persephone is with her husband in the underworld, she is sad, and that's why everything dies.

*Update: Sorry, had to fix some of that. All of this was done from memory.