After the tumultuous An Lushan Rebellion (755–763), the early Tang career path of officials rising in a hierarchy of six ministries—with Works given the lowest status and Personnel the highest—was changed into a system where officials chose specialized careers within one of the six ministries. The commissions of Salt and Iron, Funds, and Census that were created to deal with immediate financial crisis after An Lushan's insurrection were the influential basis for this change in career paths that became focused within functionally distinct hierarchies. The varied career backgrounds and expertise of early Northern Song officials meant that they were to be given specific assignment to work in only one of the ministries: Personnel, Revenue, Rites, War, Justice, or Works. As China's population increased and regional economies became more complex the central government could no longer handle the separate parts of the empire efficiently. As a result of this, in 1082 the reorganization of the central bureaucracy scrapped the hierarchies of commissions in favor of the early Tang model of officials advancing through a hierarchy of ministries, each with different levels of prestige.