An alliance is a coalition of states that coordinate their actions to deter or defend against military attack.The objectives of military alliances are:
- Most alliances are formalised in written treaties and are based on a fairly clear identification of who constitutes the threat.
- Countries form alliances to increase their effective power relative to another country or alliance.
- Alliances are based on national interests and can change when national interests change.
An example of a functioning military alliance with its specific objectives will be "The US backed the Islamic militants in Afghanistan against the Soviet Union in 1980s, but later attacked them when Al-Qaeda, a group of Islamic militants, led by Osama Bin Laden Launched terrorist strikes against America on 11th September 2001.