....
in 1 billion people - in 1820, i.e. in the history of its development;

2 billion people in 1927 - after 107 years,

3 billion people in 1960 - 33 years later,

4 billion people in 1974 - after 14 years,

5 billion people in 1987 after 13 years,

6 billion people in 1999 - 12 years later.

As you can see, the accumulation of the first billion inhabitants of the Earth took several tens of thousands of years, while the 6th billion of them appeared in the last 12 years.

Thus, the 20th century was the period of the fastest growth of the world population. The General accumulation of the human mass was pushed by the entry of an increasing number of countries into the period of sharply expanded reproduction of the population-the demographic revolution