The history view is nearly identical to the project list view.  In fact, it is identical with one exception - the history view only shows items which have been completed or parent projects of completed items.  Completed items will be displayed in a grayed out font and incomplete items will be shown in black.  Given the example above we can see that the project "Annual Report Preparation" is incomplete whereas all of the tasks are complete.

 

Most CompleteProject items should be completed rather than deleted as this allows you to keep a historical record of your projects.