OP, you've got a rough task. You struggle to find evidence because there's essentially none. Our FAQ has an extensive section on how that's so, commencing with /u/georgy_k_zhukov 's classic post. To take slavery out of sectional conflict and still get both the familiar sections (slave and free) and a civil war, you need to create an entire alternate history of the United States at least from 1776 onward. Your best bet for that would probably be to look at historians writing in the 1920s and 1930s. If you can find a copy of Avery Craven's The Coming of the Civil War it may be of help...but know that the academy has moved on and the arguments of Craven and others of similar bent are no longer held in much esteem.

Hello there. Your question seems to be related to school work, so we just want to remind you, and any potential respondents, that our rules DO permit people to ask for help with their homework, so long as they are seeking clarification or resources, rather than the answer itself. This policy is further explained in this META Thread.

Additionally, while our users may be able to help you out here, we hope that you also will take the time to check out our six-part series, "Finding and Understanding Sources", which should hopefully prove to be helpful for you as you continue in your research.