As Hwel might say, this is a dramatic story of Sto Lat cabbages and Lancre Kings. Of countries that rebel, Fools that choose their destinies, and destinies that reject their Kings. Not to mention that words create the truth, that truth is not always honest, and sometimes you have to bend them both. 
 I love the witches, Granny Weatherwax in particular, and if you'd like a good dose of headology, this is your place to start.