Early America
For most of American history, the most populous states were in the northeast, above the Mason-Dixon Line, and east of the Mississippi River. Since World War II, many people have started moving south to the Sun Belt, leaving the north, or the Rust Belt.
Reapportionment
Every 10 years, after the census, the number of representatives each state has changes, reflecting the population change. For example, since 1950, New York has lost about a third of its delegates, while California has more than doubled.
David Witten