Imagine a US president facing the following decision:

An Asian country has split into two parts. The southernmost part has a democratically elected president and a population of roughly 20 million. The northern region is controlled by the communist party and has a powerful military.

Now the northern part of the country invades the south, attempting to unify the entire country under a communist run government.  How should the US government respond?

President Truman faced this dilemma in 1950.  I am just barely old enough to recall when President Johnson faced a similar decision in 1965.  I hope I never see a future US president face a third such decision.

When I read articles on foreign policy, I am struck by the difficulty of modeling the use of military force.  We’d like to compare two counterfactuals, but in fact we rarely know what the alternatives actually look like.  You might think you know whether various past foreign policy decisions worked out well or poorly, but how can we be sure?  Chaos theory suggests that even a tiny change in initial conditions could have vast consequences in future years.  I defy anyone to create a counterfactual for post-1917 European history if the US had not entered WWI.  One can certainly create a number of plausible counterfactuals, but how could we possibly have confidence that any one alternative history is correct?

Historical events often catch even foreign policy experts by surprise.  Think of the Iranian Revolution or the collapse of the Soviet Union.  Now image trying to not just predict what is actually going to actually happen, but also what would have happened if history had been diverted onto an entirely different track.   It’s basically impossible.

Economists also have difficulty predicting events such as the Global Financial Crisis of 2008.  But at least we often know whether past policy decisions were correct or not, at least in retrospect.  Economists now understand that monetary policy was too tight in 1930 and too easy in 1968.  In contrast, the field of foreign policy is almost entirely up for grabs.  What if we had not fought the Spanish American War?  What if we had not embargoed oil shipments to Japan in the late 1930s?  What if we had not fought the Gulf War in 1991?  There are dozens of similar questions, and few reliable answers, even if the immediate impact of the decision is relatively clear.  There is too much complexity, too many “butterfly effects”, to model anything more than the immediate impact of foreign policy counterfactuals.  In some cases (such as Ukraine) even the immediate outcome was not forecast accurately, as most experts predicted a quick Russian victory.

So then what do we do?

PS.  The picture on top shows Herodotus and Thucydides

PPS.  Tom Friedman has an outstanding essay explaining:

Why Pelosi’s Visit to Taiwan Is Utterly Reckless

But while I find the essay to be highly persuasive, how can we be sure?