So stupid are we?

The most miserable nation Poland while WW2 resembles Ukraine now.　This is because the location is geopolitically inevitable. Exactly the same thing happens if the place and the time differ, as history repeats. The appearance is exactly the same as that of 100 years ago, soldiers wear military uniform, iron helmet on head and rifle gun on shoulder. 
It has caused many casualties, repeated miserable experiences, gained sufficient experience and reflected on it, but repeated the same thing again.

Armed enemy soldiers can be killed during the war, and it is not a crime. Who made this internal rule? Even if the enemy soldiers have parents, there will be a family. Why do we need to kill each other? Is there anything he can get in exchange for so much value?

Are human beings who do not even recognize such things really stupid?