Lucas (1976) challenged the foundations of macroeconomic theory (previously dominated by the Keynesian economics approach), arguing that a macroeconomic model should be built as an aggregated version of microeconomic Models while noting that aggregation in the theoretical sense may not be possible within a given model. He developed the "Lucas critique" of economic policymaking, which holds that relationships that appear to hold in the economy, such as an apparent relationship between inflation and unemployment, could change in response to changes in economic policy. That led to the development of new classical macroeconomics and the drive towards microeconomic foundations for macroeconomic theory.