Final answer:
An oligarchy is ruled by a small group of elites, possibly based on wealth or military power, while a monarchy is typically ruled by one person, usually through hereditary succession.
Step-by-step explanation:
The main difference between an oligarchy and a monarchy lies in the number of individuals who hold power and the basis of their authority. An oligarchy is a form of government where political power is held by a small elite group, which could arise from royaltym, wealth, family ties, military strength, or religious control. Conversely, a monarchy is characterized by a single person, a monarch, ruling often based on hereditary succession or some divine sanction, and holding power until death or abdication.
In an oligarchy, the ruling elite do not necessarily inherit their power but might gain it through various means like economic influence or military might. On the other hand, in a monarchy, especially a hereditary one, the power usually passes down through a family line, and the monarch has supreme authority, although some modern constitutional monarchies limit that power. An oligarchy does not have a clear single ruler, while a monarchy does with the figure being a king, queen, prince, or princess.