Step 1: Understanding the Concept:
The question asks to identify which option is not one of the essential characteristics required for an entity to be considered a state in political science.
Step 2: Detailed Explanation:
There are four universally recognized essential elements or characteristics of a state:
1. Population: A state is a human institution; there must be people.
2. Territory: A state must have a defined geographical area.
3. Government: A state must have a political organization or machinery to make and enforce laws.
4. Sovereignty: The state must have supreme authority within its territory and be independent of external control.
The options (A) Territory, (B) Population, and (C) Government are three of these four essential elements. (D) 'Political system' is a broader term that describes the type of government a state has (e.g., democratic, authoritarian). While every state has a political system, the essential element itself is 'Government'. Therefore, 'Political system' is not one of the four core characteristics.
Step 3: Final Answer:
'Political system' is not considered one of the four essential characteristics of a state.