Machine summary:
Capital chooses the labor system whose cost is lowest based on comparative calculations of labor power cost; and recruits living labor power for it by physical coercion in the geographical extent of the world labor market at a particular point in time.
Since the capitalist method of exploitation has developed and the world labor market has expanded geographically, there is a dominant labor system and a typical pattern of migration in the world economy at each epoch.
The individual stages in the development of the world labor market follow on from each other through the course of history (Potts, 1988.
Finally, Potts' concept of the "world labor market" means in fact that gross demand of labor required by capital meets gross supply of labor by physical coercion on a world scale.
Second, they assume capital can recruit freely the labor force that it needs in the world market.