Even with having existed for millions of years, the process for humans to reach 1 billion in population was long and arduous. It is only about 12,000 years ago that humans started engaging in sedentary agriculture. This allowed humans to settle and consistently produce food, rather than hunt and gather throughout.
However, it is with the Industrial Revolution that the means for exponential human population increases was created. New technology, boosts in productivity, and the use of energy allowed for a new frontier in increasing health, sanitation, and standard of living. It is also around this time – in 1804 to be exact – that the earth’s population hit 1 billion people.