Complex sentence: This situation began changing when the People's Republic of China (PRC) mandated in 2000 that computer systems sold in its territory must support GB18030, which required that computer systems intended for sale in the PRC must move beyond the BMP.
Split into simpler sentences: This situation began changing when the People's Republic of China (PRC) ruled in 2000 that all computer systems sold in its jurisdiction would have to support GB18030. This required computer systems intended for sale in the PRC to move beyond the BMP.