Tkinter multiple checkboxes after the selection from a listbox

I'm trying to generate a list of checkboxes depending on the selection in another list box. For example: in the main list box I have 3 entries: Europe, Asia, Africa. Each entry is a list of Nation within the continent I would like to see all the objects inside the list as checkboxes when I select one. For example, if I select Europe I would have as checkboxes: Italy, Spain etc etc... if I select Africa the checkboxes that appear will be Congo, Nigeria etc...

The main problem I have is the formatting of the boxes when they appear and how to get the information on the status (variable) of the box. I'm having problems because the variable indicating each box is not saved in the main script. So I do not know how to recover the value to continue with my script, Any suggestion?