Hope you do well on your paper. I can agree on all your points, the balance of power certainly shifting in terms of free versus slave states. After the war, the Republican party stengthened its hold on the electoral college and the Senate via admission of thinly populated Western states with large immigrant populations.
When time allows, perhaps you or someone else can explain if the shifting balance of power alone brought about secession.
If the conflict concerned States Rights, which states and which rights were denied?