Macroeconomics is part of whole economics. It studies the behavior and performance of the entire economic market. The macroeconomic variables such as unemployment, inflation, GDP(Gross Domestic Product), and growth rates are important components of macroeconomics. Macroeconomists can use macroeconomic variables to describe and analyze the general outline of macroeconomic changes. Macroeconomics holds that the level of national income reflects the level of production and employment in the entire society. The role of macroeconomics is to help governments and enterprises formulate economic strategies by using macroeconomic models. Macroeconomics can analyze the microeconomic factors that affect the whole economy. Basically, these data are calculated based on the total population of a country. China, India and the United States are the three most populous countries in the world. The macroeconomic variables of these countries can be clearly analyzed and compared.

The business cycle refers to the cyclical phenomenon of economic expansion and economic contraction that occurs periodically in economic operations. The stages in the business cycle include expansion, peak, recession or contraction, depression, trough, and recovery. It also known as the economic cycle or trade cycle. A recession will lead to rising unemployment. The rising unemployment rate has led to a downturn in other economically changing factors, such as GDP, production, income, and tax rates. However, during the period of economic expansion, these economic

variability factors will increase with GDP growth. There are 13 economic recessions in the United States that last longer than the Great Depression after the 1850s. According to the National Bureau of Economic Research, July 1st witnessed the longest economic expansion cycle in the history of the United States (121 months since the end of the 2009 recession), and the 34th expansion since 1854, the last time the US economy expanded It was from March 1991 to March 2001. During the 2007-2009 economic expansion of the United States, GDP grew at about the same percentage each year. During the recession period, GDP has decreased by an average of 2.8% per year. A decrease in aggregate demand will lead to an economic recession, and an increase in aggregate demand will cause economic expansion.