The War on Terror isn't a typical war against nations, but it is a world war against common enemies. Everyone is already pulling together to put forth efforts against terrorism. It just doesn't seem like what we would think of hearing WWX because the enemy isn't well defined. We aren't storming beaches or fighting a front anymore because that's not the nature of our enemy. They are small, sneaky, and attack behind our front lines where we aren't ready. They don't have strength in numbers, but use flexibility to persist, and a low enough profile to survive.