Source and Definition

• The United Nations Charter is generally considered to be the source guiding international use-of-force principles. Under Article 2 of the Charter, all conflicts between member-nations must be settled peacefully. In addition, Article 2 explicitly forbids member-nations to threaten force or actually use it to enter another member-nation's territory or otherwise destabilize its government.
  
  

UN Security Council Authorization

• Under the UN Charter, if the UN Security Council authorizes a nation to use force against another state, the force is legitimate. The most recent example of the UN's authorizing the international use of force was Security Council Resolution 1441, allowing military action against Iraq for failing to abide by the terms of its surrender in the Iraq-Kuwait War of 1991.
  
  

Self-Defense

• Under Article 51 of the UN Charter, a nation may defend itself against an armed attack as long as it reports the use of force to the UN Security Council. It must abide by any subsequent UN Security Council decisions with respect to whether it acted within accepted international principles of self-defense. It is unclear whether Article 51 requires a nation to wait until it has been attacked or can "pre-emptively" strike another nation as long as it has evidence that an attack was imminent.
  
  

Humanitarian Intervention

• Although not explicitly stated in the UN Charter, several nations believe that the world community has a responsibility to destabilize, enter and even occupy a nation when humanitarian conditions are so poor that force is the only option available. An example of this is the United Nation's authorization of the use of force in Kosovo on humanitarian intervention grounds.
  
  

Considerations

• One of the recurring debates on the international use of force has been what parties are subject to the principle. Traditionally, use of force was allowed only against national governments in the situations outlined above. Since the 9/11 attacks, however, several nations have adopted a more loose definition of use of force. According to this looser definition, nations that knowingly harbor terrorist organizations or allow non-state organizations to launch attacks into member-states' territory are acceptable targets for the use of force whether arrives via UN Security Council authorization or for self-defense or humanitarian intervention purposes.