carpetbagger (n.)

also carpet-bagger, 1868, American English, scornful appellation for Northern whites who set up residence in the South after the fall of the Confederate states seeking private gain or political advancement. The name is based on the image of men arriving with all their worldly goods in a big carpetbag. Sense later extended to any opportunist from out of the area (such as wildcat bankers or territorial officers in the West).

[A]n opprobrious term applied properly to a class of adventurers who took advantage of the disorganized condition of political affairs in the earlier years of reconstruction to gain control of the public offices and to use their influence over the negro voters for their own selfish ends. The term was often extended to include any unpopular person of Northern origin living in the South. [Century Dictionary]