Power vacuum
In political science and political history, the term power vacuum is an analogy between a physical vacuum, to the political condition "when someone has lost control of something and no one has replaced them."[1] The situation can occur when a government has no identifiable central power or authority. The physical analogy suggests that in a power vacuum, other forces will tend to "rush in" to fill the vacuum as soon as it is created, perhaps in the form of an armed militia or insurgents, military coup, warlord or dictator.
During or following a civil war there is often a power vacuum of some sort. A power vacuum can also occur following a constitutional crisis in which large portions of the government resign or are removed, creating unclear issues regarding succession to positions of power.
Historic examples include the death of Alexander the Great, the defeat of France in the Franco-Prussian War, and the decrease in power of Great Britain and France in the Middle East after the Suez Crisis.