Why did Gertrude marry Claudius?
She was afraid that Hamlet, despite being fat and scant of breath, would accept the challenge to single combat from Fortinbrasse, to the King of Denmark, and that Hamlet, as King, would get himself killed. She married Claudius as a political endorsement of him, and she used her influence with the electors to make Claudius, King. Essentially, then, Gertrude married Claudius to set him up to die. She wanted Fortinbrasse to kill Claudius instead of Hamlet.
