Wars are declared by nation states on other nation states, as in Britain declared war on Germany in 1939.
Wars can sometimes be civil wars in which different factions within a nation state go to war with each other - the American Civil War.
Wars can also be declared on undesirable objects such as illegal drugs, but usage of the word "war" is generally accepted as metaphorical and involving no military aggression.
But a War on Terror?
According to my dictionary, terror is a noun defined as "an intense, sharp, overmastering fear." How does a nation state engage in warfare with "an intense, sharp, overmastering fear?" Does "intense, sharp, overmastering fear" fight back in retaliation? Are there Geneva Conventions on warfare conducted with "intense, sharp, overmastering fear?" Can we take POWs from "an intense, sharp, overmastering fear?"
No. We cannot because terror lives within ourselves. A War on Terror is a war against our deepest, darkest fears. It is a war against ourselves.
Remember that the next time they take away a civil liberty in the name of the War on Terror.