There is a popular saying that goes like this: Power corrupts and absolute power corrupts absolutely.
A quick run through the 20th century's violence is enough to prove that.
Hitler died in April 1945. The allied forces had captured Germany, and a few embattled Japanese regiments were waging a feeble war. The conclusion was foretold. Yet the US establishment decided to drop the atomic bombs on Hiroshima and Nagasaki. This killed and wounded 250 thousands people forever. These were not forces fighting the war - they were innocent people who had no direct role in the war.
General Franco killed thousands of Spaniards who opposed him. Stalin sent millions to Siberia and got many eliminated. The Pol Pot regime in Cambodia killed fellow citizens.Many Chinese lost their lives in the Cultural Revolution.
Most of us meet many types of human beings including political leaders and it is truly impossible to find someone at a personal level who wants to indulge in genocide. But the same leaders become power-hungry and do not mind ordering mass eliminations.
It is only power and nothing else that transforms ordinary people into cruel despots. It changes their psyche. They rationalise all their inhuman actions with glib explanations. They distance their real selves from the tragedy that their actions bring. They lose their soul. Power is the evil that captures their humanity.