Economic theory is essential for understanding history. It is difficult to interpret data without economic theory. Theory cannot come from data. All states are aggressive. All wars require economic resources. More liberal states will pursue more aggressive policies. The biggest bullies will get away with murder.
Socialism created impoverishment because that system did not understand economic theory. Command economies create messes because all factors of production are government controlled. No private ownership in factors of production leads to no savings and no production. Without private property, there are never any prices paid for anything. You cannot possibly engage in cost accounting in order to know if your activity is worthwhile or wasteful of scarce resources.
Presented at the History of Liberty seminar, 27 June 2001.