The admission of California would upset the balance of power in the Senate between the Southern slave states and the Northern free states.
The admission of California would give the Northern Free states two more votes in the Senate than the Southern Slave States. Before the admission of California the number of Senators were equal between the sectional interests.
The compromise of 1850 which allowed the admission of California as a state greatly increased sectional conflict.
In return for the admission of an extra free state the slave state got a much stronger fugitive slave act, and the removal of the barrier to slavery north of the Madison Dixon Line.
The stronger fugitive slave act cause great anger in the north increasing sectional conflict.
The idea of “popular sovereignty” as a means of determining if a territory would become a slave state or a free state increased sectional rivalry. One of the result of popular sovereignty was the conflict in Kansas. This conflict dubbed Bleeding Kansas was a contest to determine if the nation would become slave or free.
The application and resulting admission of California as a state set off the conflict and crisis that would in the end spark .