Why did the southern states want to leave the US and form their own country?

The southern states sought to leave the US and form their own country primarily due to the issue of slavery, which they viewed as essential to their agricultural economy and social order. Tensions escalated over states' rights and the federal government's increasing opposition to the expansion of slavery into new territories. Additionally, cultural and economic differences with the northern states fueled desires for independence, leading to the formation of the Confederacy in 1861. Ultimately, the desire to preserve their way of life and maintain control over their own affairs drove the secessionist movement.