Hi khigh,

Khan Academy is always working on adding and improving upon content, so exercises and quizzes are bound to be added to the rest of the World History content sometime! I'm not sure of when this will be though. 

If you would like to stay up-to-date on the additions and updates to the content, make sure to keep an eye on the News and Updates forum: https://khanacademy.zendesk.com/hc/en-us/community/topics/200170394.

Hope this helps! Please let me know if you have any further questions!