"Wrong as we think slavery is, we can yet afford to let it alone where it is, because that much is due to the necessity arising from its actual presence in the nation; but can we, while our votes will prevent it, allow it to spread into the National Territories, and to overrun us here in these Free States?"
Excerpt from Abraham Lincoln's Cooper Union Speech
Why did Lincoln express concern that slavery would overrun the Free States? What was the historical context for that statement? What did Lincoln see as the path leading to slavery overrunning the Free States?
Yes, I have done some study on what the answers to those questions are. At this point, I will just refer you to the Lincoln/Douglas debates