Final answer:
Command systems in the Soviet Union and pre-reform China mainly failed due to excessive government intervention. Centralized government planning created inefficiencies and stifled innovation, as market incentives were absent.
Step-by-step explanation:
Command systems in the Soviet Union and pre-reform China failed primarily because of Excessive government intervention. These command economies, where a nation's government exerts control over the economy centrally, had very intensive planning mechanisms such as five-year plans that determined production, distribution, and the use of resources. However, this centralized planning often led to inefficiencies and a lack of innovation, as the absence of market mechanisms removed the incentives for improvement and adaptation which are typically present in market economies. Moreover, the concentration of power in the government discouraged the dispersion of decision-making, which could lead to more responsive and locally adapted economic outcomes.