Question

Why might some communist nations have adopted market principles after the fall of the Soviet Union?

Answer 1

The government system of the Soviet Union during Cold War was communism, which basically abolishes the right of an individual to own a private property. This means that the government has the sole control in all of its resources, thus a greater chance of accumulating and safe-keeping of wealth. Furthermore, during those times war among nations was already at a set off so there was a need to advance their artillery system and other equipment needed to armed themselves in case of attacks. Therefore, most of their resources went to defense spending. 

This lead to the understanding among the Soviet Union's people that the current government system was already  inefficient and is not viable to sustain the needs of their country. People then demanded a change.