A military alliance is a legally binding treaty between two or more parties in which the contracting parties agree to mutually protect one another militarily in case of an armed conflict. Military alliances differ from coalitions, which are formed in response to a specific crisis and last until the crisis is resolved. Military alliances can be bilateral or multilateral. Numerous forms of military and defensive alliances have existed between states since early human history. This is a comprehensive list of former and present military alliances.