Because the vast new territories, including California, sparked-off a fierce debate about the admission of new slave-states, which the South was demanding in order to maintain its voting power in Congress.
For California to be admitted as free soil, Congress had to appease the South by agreeing to employ official slave-catchers to hunt down runaways and return them to their owners.
This infuriated the increasingly powerful Abolitionist lobby, and the whole debate became dangerously overheated through the 1850's.
Yes.
The vast new territories, especially California, rendered invalid the successful Missouri Compromise of 1820, so a new deal had to be worked out. This one did not hold.
The balance of power! When states were founded, they had to be either slave states or free states! When California joined the Union, the South had to fight to keep control over their slaves!
Hope that helps
----ummm no. that's wrong. it is ACTUALLY because it brought the slavery issue back up which the north opposed and the south liked