The Sui, Tang and Five Dynasties Period marked the beginning of the middle phase of China’s landlord feudalism, during which the relations of production developed rapidly. While the equal-field system continued to hold sway in the Sui and early Tang dynasties, with most land owned by the state, significant changes occurred in both land ownership and the tax system following the An Lushan Rebellion. The introduction of the semi-annual tax system, in particular, signified the decline of state land ownership, the very foundation of the equal-field system, and a growing trend toward land privatization.