If monopoly profits are to persist in the long run, the entry of new firms must be prevented by effective entry barriers. Economies of scale are the most common natural barrier to entry. Set-up costs are another natural barrier to entry. The LR adjust process that drives profits to zero in the LR does not operate in monopoly markets. In the VLR technology changes.
Innovation can break-down barriers to entry in monopoly markets.
Economist Joseph Schumpeter argued that barriers to entry were not a problem in the VLR in fact he argues that they provided an incentive for entrepreneurs to take risks associated with invention and innovation. The process of creative destruction describes the replacement of one monopolist by another through the invention of new products or production processes. Creative referred to the rise of new products. Destruction referred to the demise of the existing monopoly. Schumpeter argued that monopoly profits provide and important incentive for innovation which in turn promotes economic growth.