Why did the North control Southern politics after the war? What were the Northerners called who moved to the South?

In general, the term "carpetbagger" refers to a traveler who arrives in a new region with only a satchel (or carpetbag) of possessions, and who attempts to profit from or gain control over his new surroundings, often against the will or consent of the original inhabitants. After 1865, a number of northerners moved to the South to purchase land, lease plantations or partner with down-and-out planters in the hopes of making money from cotton.