Answer :
Slavery divided them most definitely. The North was opposed to slavery completely and the South was for slavery. Britain gained much of Canada's territory after the seven years war so America was not focused on it at this time. Instead they focused on westward expansion which then caused issues with the Native Americans because they were imposing themselves on native soil.
I believe the answer is: federal power versus states' rights
The difference regarding this issue become more intense when both parties debated the matter regarding slavery. The Democratic parties believe that the states have the right to determine the type of regulations that they want regarding slavery while the republican parties believe that the states had to conform to the federal regulations to stop slavery.