Chen Sanliang, a useless soldier in the northern part of the Qin Dynasty who couldn't even wear armor, picked up a scroll of bamboo slips without words from the pile of dead people.
This bamboo slip is picky about food - it only eats the general's soul. Every time it kills an enemy general, it swallows its soul and spits out a lost art of war.
Sun Wu's, Wu Qi's, Sun Bin's... Kill a famous general and learn a line of military science.
Chen Sanliang, a retired soldier, relied on the military skills of famous generals in the world to kill all the way from the border commander to Wu'an Jun.
He is not learning the art of war, he is trying to conquer the world.