Determining the deadliest war in human history is a complex task due to the limitations of historical records and varying definitions of "war." However, based on available data, the Second World War (1939-1945) is widely considered the deadliest conflict in human history.
The war involved a vast majority of the world's nations, resulting in an estimated 70 to 85 million fatalities, with a large proportion of casualties coming from civilian populations.
The conflict saw the use of devastating new technologies like nuclear weapons, leading to unprecedented levels of destruction and loss of life.
While other wars, like the Taiping Rebellion and the Mongol Conquests, may have resulted in higher death tolls over longer periods, the Second World War's concentrated and widespread devastation makes it the most deadly conflict in a relatively short timeframe.
The war's impact on the global political landscape, economic systems, and social structures is still felt today, making it a significant event in human history.