What are the economic and political issues raised by having an imbalance between free and slave states? Why did the balance of free and slave states matter?

Regarding the United States, the lack of balance amongst the states caused instability in the enacted separation of powers of the constitution. The House of Representatives had a higher influence inclined towards the southern states, given the Three-Fifths Compromise, and the newly acquired states' slavery status from the Mexican-American war was meant to be decided. The Kansas - Nebraska Act of 1854 allowed the population to decide over slavery, but the contrast of ideas was too great it caused internal issues, which represented fuel to the outbreak of the impending Civil War.

The balance of this status was important in order to maintain the constitutional balance of powers, limiting the existence of a majority power inside the Congress. It would also prevent confusion and bring stability in the Supreme Court, where federal trials regarding slavery would take place.