When Einstein heard of Fermi's chain reaction, he said "now everything has changed except man himself." While civilization may have reduced our tendency to commit mayhem, it has also vastly increased our capacity to pursue it if we choose to do so.
Although we generally discount the efficiency of "primitive" weapons.
The huge death toll in Rwanda was achieved almost entirely with sticks and knives.
The Romans, at Cannae, lost 50,000 killed out of 80,000 men in a few hours. That is a much higher death rate than any of our bloody Civil War battles. Such losses were not uncommon in ancient warfare.
The Taiping Rebellion of the middle 19th century against the Manchus was fought mostly with relatively primitive weapons. It is estimated that 50M people died.
Primitive weapons are ineffective when pitted against modern weapons. They can be highly efficient at slaughter when pitted against other primitive weapons or the unarmed. All you need is soldiers willing to keep killing.
And somebody to sharpen your blade every few hours.
Actually IMO nuclear weapons have done more to promote peace than anything in human history (including Christianity).
Look at history. Until the advent of nuclear weapons what two rivals such as The US and USSR would have remained at peace with each other for the time encompassing the end of WWII and the collapse of the USSR.
Mutual Assured Destruction worked and continues to work.