The economy of Bolivia has had a historic pattern of a single-commodity focus. From silver to tin to coca, Bolivia has enjoyed only occasional periods of economic diversification. Political instability and difficult topography have constrained efforts to modernize the agricultural sector. Similarly, relatively low population growth coupled with low life expectancy and high incidence of disease has kept the labor supply in flux and prevented industries from flourishing. Rampant inflation and corruption also have thwarted development, but the last years the fundamentals of its economy showed an impressing improvement leading the major credit rating agencies to an upgrade of Bolivian economy in 2010. The mining industry, especially the extraction of natural gas and zinc, currently dominates Bolivia's export economy.