International Diversification
Extending the long-run case beyond U.S. markets, and what global data adds to the argument.
Siegel extends the book's core argument beyond U.S. markets specifically, examining long-run equity returns across other developed markets and finding a broadly similar pattern — a persistent long-run equity premium over bonds and cash — while also documenting that individual countries have, at various points in history, experienced periods of severe or even total equity market disruption (major wars, revolutions, hyperinflation) that a purely U.S.-centric dataset would not capture.
This produces a nuanced practical conclusion rather than a simple one: the long-run equity premium the book documents for the U.S. appears to be a broader, more general phenomenon across developed capital markets, which supports the book's core thesis beyond just American history — but the same international data also demonstrates that no single country's market history is guaranteed to avoid a severe disruption, which is itself an argument for genuine international diversification rather than concentrating a long-run equity allocation in any one country's market alone, even a historically strong one like the U.S.
Siegel is candid about a limitation this international comparison exposes: the book's headline U.S. data, however long its span, describes a market that happened to avoid the kind of catastrophic, permanent disruption (total war on home soil, revolution, currency collapse) that some other national markets experienced during the same two centuries. This is a form of survivorship bias — the U.S. case may be somewhat more favorable than a randomly selected country's history would have been — which Siegel treats as a real complication worth being honest about, rather than grounds for dismissing the U.S. findings, since the broader multi-country data still shows a persistent equity premium even after accounting for it.
- The long-run equity premium documented for the U.S. appears in broader form across other developed markets, supporting the book's core thesis internationally.
- Individual countries have experienced severe market disruptions (war, revolution, hyperinflation) that a purely U.S.-focused dataset would not capture.
- Survivorship bias is a genuine, honestly-acknowledged limitation of the U.S. data — a real argument for international diversification even given the strength of the U.S. market's own long-run record.