Drop-down menu postback changes the choices of another dropdown menu using C#

I am kinda new to the asp.net, and I am trying to do a drop-down menu that by changing the country for an example it changes the choices in the state/province drop-drop down menu ex: if i am to choose the country USA , the drop down menu shall contain the names of the states, but if i am to choose France, the drop-down menu shall show the provinces of France. any help using a C# code? thank you in advance. ...