Over the last 100 years, the world's population has exponentially grown from 1.6 billion people in 1920 to an estimated 7.8 billion people today. The shift has been driven by rising birthrates, improved healthcare, and higher life expectancies in many regions. There has also been significant migration, with many countries seeing an influx of new immigrants.
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### Instruction:
Describe the changes in the world's population over the last 100 years.

### Response:
Over the last 100 years, the world's population has exponentially grown from 1.6 billion people in 1920 to an estimated 7.8 billion people today. The shift has been driven by rising birthrates, improved healthcare, and higher life expectancies in many regions. There has also been significant migration, with many countries seeing an influx of new immigrants.
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Over the last 100 years, the world's population has experienced significant changes, driven by various factors such as technological advancements, economic growth, and changes in demographics. Here are some key changes that have occurred:

**Decline in population:** The world's population has declined from approximately 3.3 billion in 1920 to 7.1 billion in 2020, according to the United Nations. This decline is largely attributed to improvements in healthcare, sanitation, and living standards, which have led to a decrease in mortality rates and an increase in life expectancy.

**Urbanization:** The world's population has shifted from a rural to an urbanized lifestyle. In 1900, only 20% of the world's population lived in urban areas, while by 2020, this percentage had increased to 55%. This shift is driven by the growth of cities and the development of urban infrastructure.

**Increased life expectancy:** The average life expectancy at birth has increased from 31.8 years in 1900 to 72.6 years in 2020. This is due to improvements in healthcare, sanitation, and living standards, which have led to a decrease in mortality rates.

**Changes in fertility rates:** Fertility rates have also changed significantly over the last 100 years. In 1900, the average fertility rate was 5 children per woman, while in 2020, it had increased to 2.3 children per woman. This decline in fertility rates is attributed to improvements in education, economic opportunities, and family planning.

**Demographic changes:** The world's population has also undergone significant demographic changes. In 1900, the global population was predominantly young, with 70% of the population under the age of 30. By 2020, this percentage had decreased to 54%. Additionally, the global population has become increasingly older, with a higher proportion of people aged 65 and older.

**Regional variations:** The changes in population over the last 100 years have been influenced by regional variations. For example, the population of East Asia has experienced significant growth, driven by urbanization and economic development, while the population of Africa has declined due to low fertility rates and conflicts.

**Global population projections:** Based on the UN's medium-variant projection, the world's population is projected to reach 9.7 billion by 2050 and 11.2 billion by 2100. This growth is driven by improvements in healthcare, sanitation, and living standards, as well as increasing life expectancy and fertility rates.

Overall, the changes in the world's population over the last 100 years have been significant, driven by various factors such as technological advancements, economic growth, and changes in demographics.