The “convergence” theory suggests that poorer states like Mississippi should have caught up to richer states like Connecticut over time. This economic projection held true in America’s history until about 1980, and some researchers blame overbearing residential zoning laws. More from the Boston Globe:
During the 100 years of high convergence, Americans moved in droves from poorer states to richer states in search of higher wages. As more people crowded into richer states, average wages there began to fall in response to the relative oversupply of workers; meanwhile wages in the poorer states began to rise for the relatively few workers who remained behind, creating a kind of economic balancing effect between American regions.
Theoretically this process should have continued until Mississippi and Connecticut were more or less equally desirable places to work and Shoag and Ganong propose a three-step explanation why it did not: Convergence stopped because labor migration stopped; labor migration stopped because housing prices in the richest states grew so out of whack that low-skilled workers could no longer afford to move in; and housing prices skyrocketed in response to zoning laws written in the 1970s that artificially restricted the amount and type of housing that could be built in richer locales.