Mill's concept was refined and developed by nineteenth-century economist Henry George in his book Progress and Poverty (1879).
A landowner's exclusive claim to their land granted them the ability to collect the excess productivity as economic rent.
Thorstein Veblen further developed the concept, pointing out that the value of a piece of land was also dependent on current technological capabilities.
[2] Veblen thought the unearned increment increased as the industrial arts advanced, so the argument could be extended from land to capital goods.
[2] For both George and Veblen, the unearned increment emerges from the actions of an individual with the ability to exclusively use a community asset in order to generate profit.