Why did southern democrats walk out of the democratic convention?

They supported slavery but lost the platform vote against northern democrats and left the convention  

Explanation:

The southern democrats and northern democrats had different views about the slavery. The southern democrats supported slavery whereas the northern democrats wanted to support the popular sovereignty in matters of slavery. Due to this, a platform vote was held which was won by the northerners. When the southern democrats realized that the decision about the slavery will not be made on their favor.Following this situation, 50 southern delegates walked out of the demographic convention.