A more thorough explanation:

Definition: Proportionality is a principle in international law that states that the use of force should be proportional to the threat or grievance that provoked the use of force.

Example: If a country is attacked by another country, it may respond with military force to defend itself. However, the principle of proportionality requires that the response be proportional to the threat. For example, if a small group of militants attacks a military outpost, it would not be proportional for the attacked country to respond with a nuclear bomb.

Explanation: The principle of proportionality is meant to prevent excessive use of force in response to a threat or grievance. It requires that the response be proportional to the situation at hand. In the example given, a nuclear bomb would be excessive and cause unnecessary harm to civilians and the environment. Therefore, a proportional response would be a military operation to neutralize the militants and protect the outpost.