In the early Western Han, a wealthy salt or iron industrialist, whether a semi-autonomous king or wealthy merchant, could boast funds that rivaled the imperial treasury and amass a peasant workforce of over a thousand. This kept many peasants away from their farms and denied the government a significant portion of its land tax revenue. To eliminate the influence of such private entrepreneurs, Emperor Wu nationalized the salt and iron industries in 117 BC and allowed many of the former industrialists to become officials administering the monopolies. By Eastern Han times, the central government monopolies were repealed in favor of production by commandery and county administrations, as well as private businessmen.

In which year did Emperor Wu monopolize several industries?