Theory of economic growth was a combination of economic work done by Adam Smith, David Ricardo, and Robert Malthus in the eighteenth and nineteenth centuries. The theory states that every economy has a steady state GDP. Any deviation off of that steady state is temporary and will eventually return. This is based on the concept that when there is a growth in GDP, population will increase. The increase in population thus has an adverse effect on GDP due to the higher demand on limited resources from a larger population. The GDP will eventually lower back to the steady state. When GDP deviates below the steady state, population will decrease and thus lower demand on the resources. In turn, the GDP will rise back to its steady state.