Final answer:
The government form that involves a union of several countries with shared power is a confederation, whereas a republic is characterized by elected representatives without a hereditary ruling class. Monarchies and oligarchies represent rule by one or an elite few based on hereditary or elite status.
Step-by-step explanation:
Forms of Government and Power Structures
The form of government consisting of a union of several countries with some or most power shared between them is known as a confederation. A confederation is characterized by a weak central authority with the majority of power retained by the individual member states. This was the initial system adopted by the American revolutionaries under the Articles of Confederation before transitioning to a federal system with the drafting of the Constitution.
On the other hand, in a republic, there is no hereditary ruling class, and the government operates on the principle of popular sovereignty with elected representatives. In contrast, a monarchy is typically a system where a single person rules based on hereditary succession or divine appointment. However, some monarchies, like constitutional monarchies, may operate with an elected legislature. An oligarchy is a form of government where political power is concentrated in the hands of a small elite group.