Final answer:
In 1900, the global population was about 1.6 billion people. This number significantly increased from less than a billion in 1800, and by 1960, it had risen to 3 billion due to lower death rates and high birth rates.
Step-by-step explanation:
The world's population at the beginning of the 20th century, specifically in the year 1900, was approximately 1.6 billion people. This number reflected a significant increase from 1800 when there were fewer than a billion inhabitants. The following decades witnessed an exponential increase in population due to advancements in healthcare and agriculture, leading to lower death rates and sustained high birth rates in developing countries.
By 1960, the population had nearly doubled to 3 billion. The 20th century saw a dramatic population increase, with the population doubling times gradually shortening, which illustrates the rapid pace of growth.