Why was it important to keep the balance between slave and free states

The continuation of the balance between slave and free states was important given the nature of the Congress and the balance of power between the competing sides in the issue. ... Compromises were needed to equalize the power between proslavery and antislavery interests in the government to keep the Union together.

i think they would live in caves or natural tunnels

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).