Final answer:
Southerners were unhappy about California's application to the Union as a free state because it would upset the balance of power and potentially lead to the prohibition of slavery. They found it problematic because it undermined their economy and way of life, and could set a precedent for more free states.
Step-by-step explanation:
Southerners were unhappy about California's application to the Union as a free state because it would upset the balance of power between free and slave states. The admission of California as a free state would tip the balance in favor of the Northern states, threatening the Southern states' political influence and potentially leading to the prohibition of slavery in new territories.
Southerners found this problematic because it would undermine the institution of slavery, upon which their economy and way of life depended. Slavery was crucial to the Southern agricultural economy, and they feared that the growing antislavery sentiment in the North would eventually threaten the institution in the Southern states as well.
Furthermore, Southerners were concerned that the admission of California as a free state would set a precedent for other territories to also be admitted as free states, further diminishing the influence and power of the Southern states.
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