A carpetbagger was historically a pejorative term for Northerners who moved to the South during the Reconstruction period in the late 19th century, following the US Civil War. In common usage, the term is still usually used as an insult, although historians use it freely to describe this group of people, without any intended derogatory meaning.
In the 19th century, as populations throughout the United States and Europe became much more mobile, there was a growing need for a cheap form of luggage. A number of businesses began buying old carpet at low prices, and turning them into cheap and easy bags. These were known as carpetbags, and were widespread among the lower and middle classes in the United States in the period around Reconstruction. A person who carried such a bag to move from the North to the South was known as a carpetbagger.
The Civil War brutalized the South of the United States, and during the Reconstruction period, poverty was rampant. Foreclosures were widespread, and prices were extremely low for virtually everything. In many ways, the South immediately following the war was similar to a Third World country in the modern world, with a depressed economy and little upward mobility.
This provided a unique opportunity for middle-class Northerners, who may not have had a great deal of opportunity in their home states. By moving to the South, however, they could take their relatively small nest egg and use it to buy a large farm or old plantation, and hire on freedmen or white workers at a fraction of what such labor would have cost them in the North.
Some of the worst abuses taken by a carpetbagger were those of political exploitation. By taking their money, corrupt politicians from the North could move South and spread what was a relatively great deal of wealth as bribes and graft to rise to prominence and exert undue control over their new home’s political structure. Largely because of this political exploitation, the term became incredibly pejorative, and was eventually used in the South to refer to any Northerner who was seen as moving South to take undue advantage of the economic disparity between the two regions.
Not everyone called by this name was necessarily moving South for their own gain. A number of politicians moved in order to spread their abolitionist and reformist ideals, pushing racial equality through local politics that they were able to affect to a greater degree because of their relative wealth. Many reformists also moved to use their wealth to start schools for freed slaves, most of whom were not cared for by the local governments.
Perhaps the most iconic carpetbagger in literature is The King from Mark Twain’s The Adventures of Huckleberry Finn who, along with The Duke, came to the South as con men to take advantage of Southerners.
In modern usage, "carpetbagger" has come to mean anyone who comes to an area to take advantage of it politically when he or she was not originally from that area. Party zealots who may move to a new district to run for an office they believe they can use their wealth to win are often referred to in this way. Bobby Kennedy, for example, was sometimes referred to as such by his detractors after moving to New York in order to run for the Senate. The term is also sometimes used to refer to George W. Bush, due to his move to Texas after being born and educated in Connecticut.