Dear Professor Ransom,
In a response notably snarky for its insistence that your reader has ignored facts, you got some numbers way wrong. You wrote that the total number of people who had lived up to 1900 was only 1.06 billion. One point oh six billion.
The correct figure, no doubt the figure you thought your source gave, is 106 billion. One hundred billion plus change. (A little internet search on "number of people who have ever lived" would have got you this stat.)
Your claim for the number of people killed in earlier wars is also wrong. Steven Pinkers' "The Better Angels of our Nature" gives details. Billions died in wars prior to the 20th century.