A just war can only be waged as a last resort. All non violent options must be exhausted before the use of force can be justified.
We have not used all possible remedies to end the war on terrorism. For instance, we have not yet found Bin Laden and tried him for his actions. This would be a safer and more peaceful way to go about ending this war. Also we should give diplomacy more time. I feel that there are many other ways to fight terrorism without result