Client state refers to the notion of one state being subservient to another. This can occur in many varying ways, most commonly by treaty, military occupation, and/or economic dependence. Client states have existed for millenia as stronger powers made subservient those around them as they grew. In ancient times states such as Persia and Greek Polis' would create client states by making the personal leaders of that state subservient. One of the most prolific users of client states was Republican Rome which, instead of conquering and then absorbing into an empire, instead chose to make client states out of those it defeated, a policy which was continued up until the 1st Century BC when Imperial Power took over. The use of client states continued through the Middle Ages as the feudal system began to take hold, and in a way the entire society was based upon various divisions of a realm being clients to middle level nobility, who in turn were client to the powerful nobility, who were in turn client to the monarch, who, in the case of Catholic states, was often a client of the Pope.

In modern times, client states have developed based upon imperial posessions of the great European powers of 19th Century. These client states were especially obvious during the Cold War as almost the entire world divided based upon being a client state of either the Soviet Union or the United States. In general during the second half of the 20th century, most political and some economical freedoms were higher in the Latin American client states of the USA, except for the regular use of lethal violence (death squads, rape, disappearances) rather than imprisonment; while most social and some cultural and economical human rights were better protected in the Eastern European client states of the USSR.

During the collapse of the communist and capitalist superpowers which occurred during the decades before and after the turn of the century (2000), it was hoped that the client states of the two fallen superpowers could gain true social, political and economic independence.