What made world war 2 catastrophe of epic dimensions?

World War II was a catastrophe of epic dimensions due to its unprecedented scale, involving over 100 million people from more than 30 countries and resulting in an estimated 70-85 million fatalities. The war's widespread devastation included significant civilian casualties, genocide, and the use of atomic weapons, altering global power dynamics. Additionally, it led to massive economic upheaval and the displacement of millions, reshaping borders and societies for generations to come. The conflict fundamentally changed international relations, leading to the establishment of the United Nations and the Cold War era.