For now traders are the determinants of bitcoin pricing and the forces of demand and supply are the tools in their hand. The market capitalization of bitcoin which stood at over $41b today are sign that bitcoin is not control by individuals, governments and nations.
Certainly no one control the btc prices. But as a country if we would have to say then it will be China. So majorly if they bring a transformation changes overnight in their bitcoin policies then certainly the prices will get impacted in a very big way, Else generally the price may not be significantly impacted as such even if bunch of people may come together and try to buy/sell or create a short term demand supply gap.