Paragraph- Sent 1: The series starts in Baghdad at an undetermined time .
Sent 2: The Sultan Shahryar has gone mad after accidentally killing his wife during a failed coup d' tat , which she had planned with Shahryar 's brother Schahzenan .
Sent 3: In his madness , Shahryar believes that all women now want to kill him , but the law states that the Sultan must be married again or the throne will be passed to his brother .
Sent 4: Shahryar therefore orders Grand Vizier Ja'Far ( ( ( Jim Carter to bring him a harem girl to marry and then have executed the next day .
Sent 5: In order to prevent this , the Grand Vizier 's clever daughter , Scheherazade , decides to marry the Sultan herself .
Sent 6: Scheherazade has a plan to prevent her execution and at the same time cure the Sultan of his madness .
Sent 7: With the help of some tutoring from a bazaar storyteller , Scheherazade tells the Sultan a story every night , stopping at dawn with a cliffhanger and refusing to continue until dusk .
Sent 8: Shahryar must therefore let Scheherazade live for another day in order to hear the rest of the story .
Sent 9: Cunningly , Scheherazade has hidden a moral within every story , to bring the Sultan out of his madness .
Sent 10: Meanwhile , Schahzenan hears about the Sultan 's madness and that he is unable to execute Scheherazade .
Sent 11: Perceiving this as weakness , Schahzenan leads his army to Baghdad in an attempt to take the throne by force .
Sent 12: However , by the time Schahzenan 's army reaches the city , Scheherazade 's plan has worked .
Sent 13: As a result of her stories , Shahryar has overcome his madness and has fallen in love with Scheherazade . 
Question: Based on which weakness of Sultan, Schahzenan leads his army to Baghdad in an attempt to take the throne? 
Correct Answer: sultan's madness.