Is there a word/phrase to describe a government's leading power during wartime instability?

So in a wartime scenario where a nation's government is undergoing upheaval from various factions gaining and losing power, is there a proper word/phrase to describe "the current group in charge" in a way that encompasses all types of governmental bodies?

E.g. The Rebels coup and install some sort of Oligarchy, but 2 years later they are overthrown by a Nationalist faction who turns it into a Dictatorship - how would you describe the Rebels and Nationalists when they are in charge at their respective periods of time?

"Leading faction", "Ruling party", "Ruling power", "Sovereign" seem close but not quite it.

By the way, 'oligarchy' can be a legitimate form of government. In ancient Greece, where it originated most city states were oligarchies. They replaced 'aristocratic' rule, where those in power were so by birth, and 'oligarchy' was rule by the citizens with more than a certain minimum property, and officials were elected from them and they could all vote on laws. In that sense Britain was an oligarchy till 1917 - and women did not have it till 1928!

Solution 1:

There is a simple word for such a group: it would be a junta So, for example, the military dictatorship in Greece between 1967 and 1974 came to power by means of a military coup. Most such regimes are of limited duration. Some, like the Soviet Union' Communist Government, lasted longer and was however grudgingly referred to as the government. Even that was often referred to as a régime. This word implies that though it is established in power, it lacks proper legitimacy. How we should refer to modern China is one of the great puzzles of our time.