China and India, which are currently the first and second largest countries, have grown to become world economic powers. In my opinion, population is an economic power because business opportunities certainly require a long process from production to consumption, countries that have large populations are certainly a very useful resource and important for the economy.
China's population can be misleading. China has over 1.4 billion in population but due to its huge area, it only has 390 population per square miles. Meanwhile, India has 1,130 population per square mile which is nearly three times as many compared to China.
Huge or low population density has its cons and pros. Lower population density countries are less likely to fast-track their resources but unemployment might not be a concern. Whereas huge population density countries if utilized well can quickly exploit resources and drive their economy bigger. Failure to do so can lead to unemployment, very cheap labor, and other issues that reflect a lower GDP per capita.