What makes you think so? Read on from Rev 12:7 where "war in heaven" is referred to, and you soon come to:
Rev 12:9 "And the great dragon was cast out, that old serpent, called the Devil, and Satan,
which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him."
Rev 12:10 2And I heard a loud voice saying in heaven, Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ:
for the accuser of our brethren is cast down, which accused them before our God day and night."
This doesn't sound "OT" to me.