Democide, a modern mega-atrocity, has existed in greatest numbers under fiat regimes. According to some (Rummel), democide surpassed war as the leading cause of non-natural death in the 20th century. Fiat has been used to finance almost every dictator, every world war and internment camp in human history. In the 20th century alone, fiat-currency-funded-governments murdered over 169 million people through democide:

Power kills, and absolute power kills absolutely. Fiat literally concentrates an entire nation's power (it's economic output) into one leader.