Wars, famines and epidemics like plague cause initially expanding populations to halt or shrink, limiting the single greatest factor of production: human manual labor. Volume fluctuations in trade due to political instability are frequent; historically, trading was subject to great risk and transport of goods and raw materials was expensive, difficult, slow and unreliable. The manufacturing sector and other industries have a tendency to grow but are limited by inadequate scientific knowledge and a "backward" or highly traditionalist frame of mind which contributes to low labour productivity. In this stage, some regions are entirely self-sufficient.