It’s conventional to treat inter-war American foreign policy with a kind of contempt. This was the era of “isolationism” in which the United States is said to have engaged in the folly of believing that Europe could handle its own problems in a manner that didn’t require American interventionism. US policymakers went in for such daft notions as arms control treaties limiting the size of navies, and even the Kellogg-Briand Pact, an international agreement to “outlaw war.”
Meanwhile, if you read coverage of the global financial crisis, it seems to be the case that the consensus among economic historians is that the Great Depression was a preventable disaster. A stock market crash and a downturn of some kind look fairly inevitable, but US policymakers could have responded quickly expansionary monetary policy, the sort of bank guarantees that became the FDIC in the late-1930s, and a willingness to run federal deficits to maintain the (then rather modest) size and scope of public sector activities.
Similarly, if you look at the history of Germany, the Nazis were not an especially large, powerful, or influential political movement. Indeed, as of 1928–29, the troubled Weimar Republic looked to have substantially stabilized itself. It seems very plausible to imagine that a normal economic downturn, rather than a years-long total collapse, would have prevented the Nazis from ever coming to power.
And had that happened, is it really so implausible to think that the US foreign policymakers of the 1920s would have looked pretty vindicated? Not that all wars would have been avoided, of course, but that the era of great power wars would have ended in 1918 rather than 1945, not because of a difference in foreign policy but because of a difference in macroeconomic management? Was it really so naive of Secretary Kellogg to have not foreseen an unprecedented economic collapse years in the future leading to the rise of an unprecedented political movement?