Before the Qin's wars of unification in 221 BCE, salt was produced and traded widely and presented as tribute to the courts of the regional states. The Guanzi, a Han dynasty compilation of texts attributed to the 4th century BCE, includes a perhaps apocryphal discussion between the philosopher Guan Zhong and Duke Huan of the State of Qi on a proposed salt monopoly. The dialogue raised both practical questions about the effectiveness of taxes and moral questions about the nature of government. Guan Zhong argued that direct taxes created resentment among the people, but extolled indirect taxes, such as those on salt and iron: