The debates between Lincoln and Douglas were primarily on the topic of slavery extension.
Step-by-step explanation:
Lincoln was the Republican party challenger at the time of the 1858 campaign for the position of the senator of Illinois. This was to be the first major election campaign for Abraham Lincoln which gave him credibility enough to fight for the eventual election as president.
The debates that were happening during this election were in total seven and were debated on the issue of slavery extension into the territories of the state. Lincoln had taken a stance against the proposition of extension of slavery.