Demographers developed a hypothesis to explain the changes to the populations of countries over time. This hypothesis describes a demographic transition, in which countries change from a combination of high birthrates and high death rates to low birthrates and low death rates. The changes of the demographic transition are summarized in the graph. Birth rate and death rate are plotted against time. At first (Stage 1) both rates are high. Then in Stage 2, birth rate remains high while death rate decreases. In Stage 3, birth rate decreases to match the low death rate.

Describe the changes that a country undergoes as it passes through the three stages of the demographic transition. Use the United States as an example.