What key difference between the north and the south ultimately lead to the civil war?

Slaves and them being free

For decades the north and the south fought over several economic issues, "the second great awakening" from the people of the north meaning they started to attend many religious gatherings by the 1820's wanted to live and better and morally better life thus the abolition movement started (end slavery) other than that the north wanted to bring factories and big cities to the south but the south lived a farming lifestyle and heavily dependent on slaves, which the north abolition movement worried many southerners.