Reconstruction was the point after the Civil War where the United States was trying to reintegrate the Confederacy into the States. This caused many Southerners to become bitter and hateful, as they wanted to continue slavery even after they had lost the war.
Scalawags were Southerners who were working with the Reconstructionists and the Union, which most Southerners saw as traitorous. They felt as if these scalawags were going behind their backs and their state governments to work with Reconstructionists and free blacks. During this time, a lot of the Southerners were against African Americans having rights, so when scalawags were working closely with them to help them, they resented them for it.
Carpetbaggers were people from usually the North who traveled to the South to make a quick profit. Many of these carpetbaggers ended up helping newly freed blacks, as many had nothing else to do after they had left their plantations. Many Southerners felt as if carpetbaggers were using the devastation and collapse of the South to their advantage and also resented them for that.