Is the US Preparing for War?

There has been a lot of buzz in the last two weeks from American websites about people from the four corners of the US claiming to have been witness to an increase in military presence with large fleets rolling through their towns. Four mile long convoys have been reported with everything from large numbers of oil trucks to dozens of military hummers to desert tanks. FEMA drills have also been on the increase recently as per various sources.
Assuming this is not the result of an increasingly paranoid society, whatever the cause might be, the American public would appear to be left in the dark at the moment, though awareness of its presence is obviously growing.

Could it be part of drills connected to a new type of home-grown disaster military commander, or be connected to Libya/Syria, or possibly North Korea? Or some kind of large scale terrorist threat? Or marshal law? Or maybe just regular day-to-day military exercise? One can only guess and hope there is no sinister motive behind all of this.