1). How do you support that view - dates, battles, synopses, analyses and outcomes of events and your understanding of the key attributes/failings of the main protagonists (i.e. Lee & Jackson)? You might want to toss in an overview of the political aspirations and problems faced of the two respective presidents of the Confederacy and the Union.
2). What events support your proposition?
3). In which way did "the south beat itself" - what argument or information can you offer which supports your view?
If you can open with a supported proposition, you've every chance of others wanting to join in the debate.