and he wouldn't have it. It would be practically impossible to sow so much
dissension to an modern army, which most likely consist of people from same
nation, in such a short notice. He would have to overcome things like
nationalism, fear (modern army could defeat Morgoth's armies easily but when
fighting each other many would get killed) and general common sense. It would
be possible if he had several years or decades time, but a couple moths
wouldn't be enough.
Same goes for technology. While Sauron is hanging in research labs for several
years or decades, the army would have destroyed Morgoth. Besides most likely
Sauron wouln't have any idea of how modern technology works, if he did, then
technology would have been used against elves. (not just catapults but nukes)
In addition to this, technology can't be controlled with a master device.
(unless all devices would have a built-in remote conroller and required
hardware for automatical use, which would be
unlikely)