What it used to be called:
Technology and military strategy.
Conventional warfare pits one military force against another, each armed with traditional guns and explosives.
Unconventional warfare, spawned during the last century, features biological, chemical, or nuclear weapons; it's also applied to counterinsurgency and guerrilla fighting.
An early use:
"The ground forces must make the most revolutionary changes in tactics and thinking to face atomic war... Some top-ranking military leaders fear the changes may be too revolutionary, leaving the ground forces unprepared for conventional warfare." Life, July 25, 1955