To declare war on “international terrorism” is nonsense. Politicians who do so are either fools or cynics, and probably both.
Terrorism is a weapon. Like cannon. We would laugh at somebody who declares war on “international artillery”. A cannon belongs to an army, and serves the aims of that army. The cannon of one side fire against the cannon of the other.
Terrorism is a method of operation. It is often used by oppressed peoples, including the French Resistance to the Nazis in WW II. We would laugh at anyone who declared war on “international resistance”.
Carl von Clausewitz, the Prussian military thinker, famously said that “war is the continuation of politics by other means”. If he had lived with us today, he might have said: “Terrorism is a continuation of policy by other means.”
Terrorism means, literally, to frighten the victims into surrendering to the will of the terrorist.
Terrorism is a weapon. Generally it is the weapon of the weak. Of those who have no atom bombs, like the ones which were dropped on Hiroshima and Nagasaki, which terrorized the Japanese into surrender. Or the aircraft which destroyed Dresden in the (vain) attempt to frighten the Germans into giving up.
Since most of the groups and countries using terrorism have different aims, often contradicting each other, there is nothing “international” about it. Each terrorist campaign has a character of its own. Not to mention the fact that nobody considers himself (or herself) a terrorist, but rather a fighter for God, Freedom or Whatever....