North vs South

As the US began to expand, tension between the North and South increased. At the time, representation in Congress was equally split between the two groups with 15 slave states and 15 free states. With no majority, there could be no movement for or against slavery in the nation. With the acquisition of new land after the Mexican War, the inevitable question over the legality of slavery would arise. When new states joined the nation, either the free states or slaves states would gain the upper hand, and both sides were afraid of this possibility.