Why did southern slave owners fear nothern attitudes toward slavery?

Southern slave owners feared that Northern attitudes toward slavery, which were increasingly abolitionist, would threaten their economic and social system based on slave labor. They worried that Northern efforts to limit the expansion of slavery into new territories would eventually lead to its abolition in the South. This fear stemmed from the understanding that Northern abolitionist sentiment posed a direct challenge to the institution of slavery that was foundational to the Southern way of life.