The one thing you need to know!
The population of the world did NOT hit 1 billion until the early 1800s. Since that time it multiplies by over seven! The Industrial Revolution (1700s-1800s) equals more food, which equals more people in the developed world.
The Medical Revolution/Green Revolution (1900s) equals people living longer and more food, which equals more people in the developing world.
Contextualizing the Unit
Pre-Industrial Revolution the population of the world rises slowly and steadily. Once factories are able to mass produce tools and new farming techniques are utilized a second agricultural revolution occurs and the population in the developed world (Europe and North America) begins to skyrocket!
By the mid 1800s population growth seems to be out of hand and some experts (e.g. Thomas Malthus) conclude that the world is destined to have cataclysmic famine and starving, which does NOT happen, but there are negative consequences in some parts of the world.
In the 1900s the Medical Revolution drastically cuts down on maternal mortality rates and infant mortality rates. Thus more children survive, which reduces total fertility rates. The Green Revolution, spearheaded by American agronomist Norman Borlaug, makes growing strains of grain much easier around the world. Because of this, more food is available in developing countries, which causes the population in Africa, Asia and Latin America to spike.
With so many people in the world, people move from their place of birth for a myriad of reasons. The number one voluntary reason is for better economic opportunities. This is why people move from developing countries to developed ones. People are forced from their homes because of war, poverty, environmental reasons (flood, drought, global warming, etc.)
1760~1840: Industrial Revolution
1798: Thomas Malthus publishes ‘An Essay on the Principles of Population’
1804: Population of the world hits 1 billion
1845-1849: Irish Potato Famine, United Kingdom uses Malthus’ theory as the basis to not help the Irish
1854: Epidemiologist John Snow links the cholera outbreak in London to a tainted water pump
1927: Population of the world hits 2 billion
1955: Jonas Salk develops a polio vaccine
1960: Population of the world hits 3 billion
1970: Norman Borlaug wins Nobel Peace Prize for his wheat strand
1974: Population of the world hits 4 billion
1987: Population of the world hits 5 billion
1999: Population of the world hits 6 billion
2011: Population of the world hits 7 billion
2023-2024: Demographers believe the population of the world hits 8 billion