The necessary condition for development in underdeveloped economies is a rate of growth of capital higher than the rate of growth of population.
There is always some possibility, in these economies, of raising the rate of growth of capital in the non-disguised unemployment sector. There may be some possibility too of raising the rate of saving in the disguised unemployment sector. But if the increase is not sufficient for the rate of growth of capital to exceed the rate of growth of population, the factors strategic for development then become the rate of inflow; of capital, population planning and socialism.
The policy implications of this analysis are discussed here.