I don't own the Inheritence Cycle series.
I invite you to use anything you want from this story to write one of your own.
After the death of Galbatorix Eragon spent two hundred years exploring the world before he returned to Alagaesia.
The state of the land changed massively. The elves were now the most powerful faction. Not in numbers but in power.
Their new king Franir had married Arya forty years ago. He was charismatic and cunning. All the elves and many humans followed him with devotion.
Franir saw Eragon as a threat and used his guile to create a wedge between Eragon and his wife Arya. It wasn't very hard to fan Eragon's jealosy since he still loved her and resenterd her for choosing Franir as her husband.
With the help of a few misunderstandings and subtle manipulations Franir created a conflict between Eragon and the elves.
Eragon with his idealism and naivity walked right into a trap. He was only able to survive because Saphira sacrificed herself for him.
Her death created a hole inside of him that he could never fill again.
After years of hiding scheming and nourishing his hatred, he plunged Alagaesia into a new war. He rallied the dwarfs and the urgals against the elves and humans.
The brutal and long war ended with the extermination of the elven race.
Even throgh Eragon got his revenge he didn't feel better at all. This time he stayed to help create a new order. They created a council of humans, dwarfs and urgals to rule Alagaesia.
He made sure they had a stable government and left to built a retreat for himself in the mountains.
He filled his days with farm work to sustain his needs and magical experiments to pass the next century.
When Eragon rejoined the world he quickly noticed the corruption that the new state of affairs had bred.
Thousands of years passed him by in an endless cycle. He built kingdoms and governments in Alagaesia and then watched them fall. Most corrupt ones he destroyed himself through various means. Some collapsed on themselves or for other reasons.
So he stopped caring altogether and only concerned himself with Alagaesia's people when he was in a mood to play with them. Eragon adopted countless hobbies over the years but the one constant always his research of magic and the secrets of the world.
Everything changed when Eragon found the power of magical rituals. Years went by till he mastered this aspect of magic. He created his masterpiece.
Eragon went and enslaved the whole population of Alagaesia to sacrifice them in his ritual.
Rivers of blood fueled his ambition.