In the Lincoln-Douglas debates of 1858, Abraham Lincoln, a member of the Republican Party debated against Stephen Douglas, a Democrat, for the title of Senator of Illinois. Seven debates took place throughout Illinois with one main topic: slavery.
A very interesting article from History by Hilary…
More information on the Lincoln-Douglas Debates:
A map of the debates, their location and dates – http://www.nps.gov/archive/liho/debates.htm