The correct answer is California’s entrance as a free state would upset the legislative balance in favor of the North.
When California applied for statehood, there was a balance of voters in Congress made up of two groups: one group who was in favor of the expansion of the institution of slavery and another group against the expansion of slavery.
To keep these groups from fighting, many different compromises were made throughout the 1800's in order to help keep the peace. An example of this would be the Compromise of 1850. In this compromise, California is admitted as a free state. However,the Southern states get a stronger fugitive slave law in return. This fighting over a balance of power between slave states and non slave states was one of the most significant causes of the American Civil War.
