As far as the state is concerned, if it wants to wage a defensive war against any country it has first—in obedience to the Quran—to issue a proper declaration. Only then can it wage a lawful war (8:58). In Islam, there is only ‘declared’ war. Therefore, in accordance with this principle, no proxy war in Islam can be lawful.
Most Islamic actions are governed by certain conditions. The waging of war is also thus subject to certain principles, one being that, even when a defensive war has been declared by the State, it will be aimed only at the combatants. Targeting non-combatants will be unlawful. The Quran enjoins us not to do battle with those who are not at war. Such people have to be dealt with kindly and equitably. But you are free to do battle with those who are fighting against you. (60:8-9)
If, for instance, a Muslim state is at war with a particular nation, and this war is in conformance with Islamic principles, it should still not permit any destructive activities against non-combatants (civilians), as was done on September 11, 2001, in New York and Washington. Similarly in Islamic war, Muslims are not permitted to commit suicidal bombings in order to destroy the enemy. Strapping explosives on to oneself and hurling oneself upon the civilian settlements of even those with whom one is at war, for the purpose of destroying the enemy, and in the process killing oneself deliberately, is totally un-Islamic.
Because of the importance of peace, the Qur’an has clearly declared that no aggressive war is permitted in Islam. Muslims can engage themselves only in a defensive, not in an offensive war, irrespective of the circumstances (2:190).
According to Islam, peace is the rule and war is only an exception. Even in defensive war we have to see the result. If the result is doubtful, Muslims should avoid war, even in a defensive situation. Stray acts of aggression are not enough for Muslims to rush into war. They have to assess the whole situation and adopt a policy of avoidance when war is not certain to achieve a positive result.