Until the 19
th century, population growth across the globe was incredibly low. In the first millennium of the Common Era, the world's population grew by an average of just 0.02 percent each year. In Western Europe and Asia, the populations on either side of the millennium were almost the exact same. It was only in the centuries that followed where population growth began to increase, however it was still very low until the 1800s.
Beginning in the 19
th century, a phenomenon known as the demographic transition took place, and the
world's population began to grow exponentially. The population of the Americas in particular saw the highest average growth rates in these years, due to the high levels of migration and their smaller starting population size in 1820 compared to most other regions. Overall, the average global population growth rate in the period between 1820 and 1998 was roughly six times higher than the preceding eight centuries, and almost 50 times higher than the millennium before that.