Traumas suffered by a society generations ago can still have a negative effect centuries later.
This is something Americans of a certain age should have no difficulty understanding. Half a century ago, we had to grapple with a dysfunctional and unjustifiable system of legally imposed racial segregation. It was a legacy of the Civil War a century before and of slavery before that.
Americans managed to reform that system, but it wasn't easy. Getting rid of policies that are the responses to long-ago traumas is a difficult business.
Two current instances, one facing America and the other facing Europe, come to mind. Both result from strong desires to learn from the mistakes made in the years following World War I -- the Great War, as it was called at the time -- which began nearly a century ago.
The first case involves American immigration policy. Many Americans were uneasy about the millions of immigrants who had flowed in from Eastern and Southern Europe in the years after the opening of Ellis Island in 1892. World War I showed them that government could control the flow of people, and in 1924, Congress cut off the flow of Ellis Islanders.
This came to seem an injustice, especially to their descendants, and in 1965, Congress rewrote immigration law to allow large-scale low-skill and family-reunification migration. It was an attempt to atone for a mistake made in the wake of war.
But like most reforms, it had unintended consequences. Large-scale immigration came not from Europe, as expected, but from Latin America, especially Mexico, and also from Asia. The United States failed to keep illegal immigrants from crossing the land border with Mexico, and Congress rejected a national identity card that might have prevented illegals from getting jobs. By 2007, we had 12 million immigrants, and the controversy over what to do about them frustrated attempts to rationalize immigration law.
Now some illegals are returning home, but we still have a system that favors extended-family reunification over the high-skill immigrants whom Canada and Australia have been favoring for years. Decisions made years ago leave us with a dysfunctional immigration system.
Europe's historic problems and current plight are worse than ours. The extremist nationalism that led to the two world wars left postwar reformers like Jean Monnet convinced that European unity was necessary to prevent a third.
European elites, with minimal consultation with voters, created the Common Market, originally a free-trade area, which became the European Community, in which Brussels busybodies override national authorities on all sorts of domestic legislation (must fruit be priced by kilo rather than pound?).
Not content with this, EC leaders in 1999 launched the euro, a single currency for 17 of the now 27 nations in the European Community.
The problem is that a single currency for 17 nations with different fiscal policies ensures that some nations' economies will overheat and produce financial collapse. Eurozone leaders tried to prevent that with rules mandating harmonious fiscal policy, but allowed cheating from the start.
I won't try to describe the successive rescue packages, which seem to inspire confidence for a few days and then are rejected in financial markets. My eyes glaze over reading the details.
What seems plain is that the euro isn't workable and that the protracted euro crisis is the inevitable product of policies that arose from the heartfelt yearning not to repeat the horrors of 1914 to 1945.
In looking at both of these painfully unresolved issues, it seems that a determination not to repeat the mistakes -- in some cases, the horrifying mistakes -- of the past has made policymakers and publics timid about adjusting to changes in the future.
America's illegal immigration problem could be alleviated with identification technology that no longer seems scary. And as the illegal numbers seem to be declining, we could leave that issue aside and provide more openings for the high-skill immigrants we plainly need.
As for the euro, by the 1990s, it was plain that Germany and France were never going to war again -- and that Brussels bureaucrats could never bludgeon or cajole them, much less their Mediterranean neighbors, into following identical economic or fiscal policies.
In the meantime, credit card technology and financial innovation have made it easier to deal with different currencies.
The lesson: Heed history, but keep an eye out for changes that make historical lessons obsolete.