"The prime minister must start from the State Council, and the warrior must start from the pawn." Every general starts with a soldier. The ancient soldier promotion system was not as perfect as it is now. Soldiers want to rise, mainly by killing the enemy.
In ancient times, the reward was based on the number of enemy heads and prisoners obtained after killing the enemy. There is a plot in Hanwu the Great, in which Li Guang's friend asked Emperor Wu that Li Guang was very successful and qualified. Many people who are far less than Li Guang have been appointed. Why can't Li Guang be appointed? Emperor Wu of the Han Dynasty said, "The title of Marquis is evaluated according to the number of enemies killed and the number of prisoners captured, not by seniority." That's what it means.
Many historical records record that many people were beheaded after the war. After the war, the more heads soldiers handed in, the greater the reward they got. However, this system also has serious defects. Who can kill enemies and collect heads at the same time?
During the Qin dynasty, the war between countries has developed into a melee of hundreds of thousands of people. The more beheadings you get, the more rewards you get. So many soldiers began to use their brains. After each war, the surviving soldiers began to collect a large number of heads, whether they were enemies or their own friendly forces. As long as the head of the dead is robbed, the way of exchanging heads for rewards is gradually enabled.
War is cruel, but this way can only stimulate soldiers' desire to kill the enemy, but both ways have loopholes. Those soldiers who were lucky enough to get military merit don't know whether they will live up to their dead comrades.