Southern states vs. northern states major issue

Slavery! There was a gigantic isue surounding the number of slave states to the number of slave-free states. The slave states feared that if there were more free states than slave states, that the free states would take over congress and create a law to free all slaves. The free states believed that if the slave states out numbered the free states, the slave states would allow slavery to all the states and punish people for freeing/helping slaves.