Answer:
2 billion people
Step-by-step explanation:
The attrition rate of the ancient tribal wars was really brutal and produced casualty rate of almost 60% of the population at the time. If the proportion which is 60% is likened to the 20th century wars and 60 percent of people were killed, this population will exceed two billion because the 20th century recorded population of up to 4 billion people and if 60 percent are wiped, then this figure will exceed 2 billion people.