Ether 13:16

And now Coriantumr, having studied himself in all the arts of war, and all the cunning of the world, wherefore he gave battle unto them which sought to destroy him;

Coriantumr had learned everything about war. He knew all the tricks of the world. So he fought against those who tried to destroy him.

Coriantumr had mastered every art of war and every strategy the world had to offer, so he fought back against those trying to kill him.