Historical data tends to display what happened in different circumstances. It tends to be biased. Imagine you are an investor in the 1880s. Would you invest in the US, that emerging country that just came through a civil war and a sovereign default ? No, you wouldn't. You're not a speculator, you're an investor. You would rather invest in titans like Russia or Germany. This would be safe for the next 40 years, right ? Historical data says so.
Would you invest in stocks ? Yes, maybe a little, but why invest much ? There is no such thing as inflation, since cash is gold, no government can inflate his money, so bonds' inflation risk is a non issue, and dealing with stocks is risky. There is no such thing as public financial reports, when you invest in a stock, you can only rely on its past price and insider rumors. And capital appreciation was not a thing on these days. Money came from dividends. You didn't buy a stock just to see its market value grow, but to earn a dividend flow. Investing was nothing more than comparing stocks yield vs safe bonds yield. Oh, and since information wasn't as fast and as safe as today, markets were all but efficient. That was a very different beast.
Well, anyway, if you wanted to invest in stocks, you chose UK, not US, because the yield was much better and UK was the #1 country in the world, not a loosy emerging country.
So, looking at historical data, our 1880s investor would not put a dime in US stocks and buy lots of British bonds and stocks, and a substantive amount of French, German and Russian treasury bonds.