Final answer:
A country ruled by one man alone can be a monarchy if the rule is hereditary, or a dictatorship if the leader has absolute authority typically gained through non-hereditary means.
Step-by-step explanation:
A country ruled by one man alone is most accurately referred to as a monarchy if the ruler is a king or queen, usually a hereditary one, but it may also be considered a dictatorship if the ruler has complete and absolute authority that was not necessarily inherited. The distinction between the two can sometimes be based on the legitimacy and traditional recognition of the ruler's role and whether there is a ceremonial or constitutional aspect to their powers. In contrast, an oligarchy is a form of government where political power is held by a small, elite group, and these members do not necessarily have to be of noble lineage. They could gain power through wealth, military strength, or other means. None of these forms of government should be confused with a democracy, where all citizens have an equal voice or vote, or a monopoly, which is not a form of government but rather a term used in economics to describe a market structure where one corporation or entity controls all supply of a particular product or service.
Therefore, when a country is ruled by one man alone, it is referred to as either a monarchy or a dictatorship, depending on the circumstances surrounding the ruler's ascendancy and the nature of their rule.