An autocracy is a system of government in which supreme power is concentrated in the hands of one person, whose decisions are subject to neither external legal restraints nor regularized mechanisms of popular control (except perhaps for the implicit threat of a coup d'état or mass insurrection). Absolute monarchy (such as Saudi Arabia) and dictatorship (such as North Korea) are the main historical forms of autocracy. In very early times, the term "autocrat" was coined as a favorable feature of the ruler, having some connection to the concept of "lack of conflicts of interests".
In the Medieval Greek language, the term Autocrates was used for anyone holding the title emperor, regardless of the actual power of the monarch. Some historical Slavic monarchs, such as Russian tsars and emperors, included the title Autocrat as part of their official styles, distinguishing them from the constitutional monarchs elsewhere in Europe.
Both totalitarianism and military dictatorship are often identified with, but need not be, an autocracy. Totalitarianism is a system where the state strives to control every aspect of life and civil society. It can be headed by a supreme dictator, making it autocratic, but it can also have a collective leadership such as a commune, junta, or single political party.
In an analysis of militarized disputes between two states, if one of the states involved was an autocracy the chance of violence occurring doubled.
Because autocrats need a power structure to rule, it can be difficult to draw a clear line between historical autocracies and oligarchies. Most historical autocrats depended on their nobles, the military, the priesthood or other elite groups. Some autocracies are rationalized by assertion of divine right.
The Roman Empire: In 27 B.C., Augustus founded the Roman Empire following the end of the Republic of Rome. Augustus officially kept the Roman Senate while effectively consolidating all of the real power in himself. Rome was peaceful and prosperous until the dictatorial rule of Commodus starting in 161 A.D. The third century saw invasions from the barbarians as well as economic decline. Both Diocletian and Constantine ruled as totalitarian leaders, strengthening the control of the emperor. The empire grew extremely large, and was ruled by a tetrarchy, instituted by Diocletian. Eventually, it was split into two halves: the Western (Roman) and the Eastern (Byzantine). The Western Roman Empire fell in 476 after civic unrest, further economic decline, and invasions led to the surrender of Romulus Augustus to Odoacer, a German king.
Nazi Germany: After the failed Beer Hall Putsch, the National Socialist German Worker's Party began a more subtle political strategy to take over the government. Following a tense social and political environment in the 1930s, the Nazis under Adolf Hitler took advantage of the civil unrest of the state to seize power through cunning propaganda and by the charismatic speeches of their party leader. By the time Hitler was appointed chancellor, the Nazi party began to restrict civil liberties on the public following the Reichstag Fire. With a combination of cooperation and intimidation, Hitler and his party systematically weakened all opposition to his rule, transforming the Weimar Republic into a fascist dictatorship where Hitler alone spoke and acted on behalf of Germany. Nazi Germany is an example of an autocracy run primarily by a single leader, but many decisions made by Hitler coincided with the interests and ideology of the Nazi Party in mind, also making an example of an autocracy ruled by a political party rather than solely one man.
Aztec Empire: In Mesoamerica, the Aztecs were a tremendous military powerhouse that earned a fearsome reputation of capturing prisoners during battle to be used for sacrificial rituals. The priesthood supported a pantheon that demanded human sacrifice, and the nobility was comprised mainly of warriors who had captured many prisoners for these sacrificial rites. The Aztec Emperor hence functioned both as the sole ruler of the empire and its military forces, and as the religious figurehead behind the empire's aggressive foreign policy.
Tokugawa Shogunate: Medieval Japan was caught in a vicious series of skirmishes between warring clans, states, and rulers, all of them vying for power in a mad scramble. While many of these lords struggled against each other openly, Ieyasu Tokugawa seized mastery of all of Japan through a mix of superior tactics and cunning diplomacy, until he became the dominant power of the land. By establishing his shogunate as the sole ruling power in Japan, Ieyasu Tokugawa controlled all aspects of life, closing the borders of Japan to all foreign nations and ruling with a policy of isolationism.
Tsarist Russia: Shortly after being crowned as ruler, Tsar Ivan immediately removed his political enemies by execution or exile and established dominance over an Empire, expanding the borders of his kingdom dramatically. To enforce his rule, Ivan the Terrible established the Streltzy as Russia's standing army, and he developed two cavalry divisions that were fiercely loyal to the Tsar; the Cossacks, and the Oprichniki. In his later years, Ivan made orders for his forces to sack the city of Novgorod in fear of being overthrown.