What is the reasoning behind Lincoln's referring to the South as "the rebellion"?

Why does he continually use this term?

Lincoln continually calls the South as "rebellion" because of his perception of the North. The rebellion happened because of Lincoln’s electoral camping, causing more economic tension between the North and South. Because of this, Lincoln and the Southerners had established the Abolition Movement, thus referred to the Southerners and their fight against the Northerners