Why did Napoleon annul his marriage to his first wife, Josephine, and instead marry Marie-Louise, the daughter of Austrian Emperor Francis I?
Now that he was an emperor, he wanted a wife of royal blood.
He was “offered” Marie-Louise by her brother, the Austrian emperor, who wanted closer relations with France.
He needed an heir to his throne and also desired a diplomatically useful spouse.
Napoleon and Josephine hated each other to the point of physical violence.
He fell in love with Marie-Louise.