Well, the US does have a population of nearly 301 million... start training everyone now and you'll be able to finish the War on Terrorism in about 10 years.
But it will leave America completely undefended, unless a sizeable force stays at home.
Good, if we crush the terrorists with an insane amount of soldiers, it'd get done sooner and we would have less casualties.
The fun part is that you will never crush the terrorists. There will always be extremists bent on killing Americans, and sadly there isn't anything that can be done about it, really.