Why did the South wanted to become its own country?

As the United States expanded westward, the South's political and economic leaders realized that in due time, more states most likely would be added to the US and soon the South would have less members of the US Congress than new states that would not be slave holding states. Although the US Supreme Court in 1857, assured the South via the Dred Scott case, that slavery was legal and constitutional, it realized that its political power in the US was being marginalized.With the election of Republican Abraham Lincoln, this added to the South's thinking that whatever Lincoln said to assure the South that he would not interfere with slavery where it existed, they did not trust him.

The President of the US, then and now wields a great amount of power. To avoid becoming a "victim" and to ensure its way of life, Southern leaders believed that secession was the way to avoid interference from the North.