Unit 4 of macroeconomics covers several key topics: 1. It introduces macroeconomics and how it emerged as a separate field due to the Great Depression. John Maynard Keynes' work in 1936 was influential in establishing macroeconomics. 2. Keynesian theory states that employment is determined by effective demand and other aggregate factors. However, economies can experience inflationary or deflationary gaps that prevent full growth. 3. Macroeconomics examines the overall output, employment, prices, and trade of a nation. It considers both static and dynamic economic conditions and models like aggregate supply and demand functions. 4. Macroeconomic problems that arise include unemployment, poverty, inflation,