The enormous damage caused by Wilson's decision to intervene in WWI.

David Stockman's speech he gave a year ago on Wilson and the "Great War" is well worth your time to read. The war and Wilson's decision to intervene were unbelievable tragedies for the entire world and the stupidity of that war and the arrogance and naivete of Wilson in large part made the 20th-century the horrible tragedy it became, not least because it unleashed 70 years of leftist barbarism:

Stated differently, the trauma of the 1930s was not the result of the inherent flaws or purported cyclical instabilities of free market capitalism; it was, instead, the delayed legacy of the financial carnage of the Great War and the failed 1920s efforts to restore the liberal order of sound money, open trade and unimpeded money and capital flows.

But this trauma was thoroughly misunderstood, and therefore did give rise to the curse of Keynesian economics and did unleash the politicians to meddle in virtually every aspect of economic life, culminating in the statist and crony capitalist dystopia that has emerged in this century.

"The Epochal Consequences Of Woodrow Wilson’s War." By David Stockman, Stockman's Corner, 1/21/15.