So, another BRIC hits the wall. Actually, I’ve never much liked the whole “BRIC” — Brazil, Russia, India, and China — concept: Russia, which is basically a petro-economy, doesn’t belong there at all, and there are large differences among the other three. Still, it’s hard to deny that India, Brazil, and a number of other countries are now experiencing similar problems. And those shared problems define the economic crisis du jour.

What’s going on? It’s a variant on the same old story: investors loved these economies not wisely but too well, and have now turned on the objects of their former affection. A couple years back, Western investors — discouraged by low returns both in the United States and in the noncrisis nations of Europe — began pouring large sums into emerging markets. Now they’ve reversed course. As a result, India’s rupee and Brazil’s real are plunging, along with Indonesia’s rupiah, the South African rand, the Turkish lira, and more.

Does this reversal of fortune pose a major threat to the world economy? I don’t think so (he said with his fingers crossed behind his back). It’s true that investor loss of confidence and the resulting currency plunges caused severe economic crises in much of Asia back in 1997-98. But the crucial point back then was that, in the crisis countries, many businesses had large debts in dollars, so that falling currencies effectively caused their debts to soar, creating widespread financial distress. That problem isn’t completely absent this time around, but it looks much less serious.

In fact, count me among those who believe that the biggest threat right now is that policy in emerging markets will overreact — that their central banks will raise interest rates sharply in an attempt to prop up their currencies, which isn’t what they or the rest of the world need right now.

Still, even if the news from India and elsewhere isn’t apocalyptic, it’s not the kind of thing you want to hear when the world’s wealthier economies, while doing a bit better than they were a few months ago, are still deeply depressed and struggling to recover. And this latest financial turmoil raises a broader question: Why have we been having so many bubbles?For it’s now clear that the flood of money into emerging markets — which briefly drove Brazil’s currency up by almost 40 percent, a rise that has now been completely reversed — was yet another in the long list of financial bubbles over the past generation. There was the housing bubble, of course. But before that there was the dot-com bubble; before that the Asian bubble of the mid-1990s; before that the commercial real estate bubble of the 1980s. That last bubble, by the way, imposed a huge cost on taxpayers, who had to bail out failed savings-and-loan institutions.

The thing is, it wasn’t always thus. The ‘50s, the ‘60s, even the troubled ‘70s, weren’t nearly as bubble-prone. So what changed?One popular answer involves blaming the Federal Reserve — the loose-money policies of Ben Bernanke and, before him, Alan Greenspan. And it’s certainly true that for the past few years the Fed has tried hard to push down interest rates, both through conventional policies and through unconventional measures like buying long-term bonds. The resulting low rates certainly helped send investors looking for other places to put their money, including emerging markets.

But the Fed was only doing its job. It’s supposed to push interest rates down when the economy is depressed and inflation is low. And what about the series of earlier bubbles, which, at this point, reach back a generation?I know that there are some people who believe that the Fed has been keeping interest rates too low, and printing too much money, all along. But interest rates in the ‘80s and ‘90s were actually high by historical standards, and even during the housing bubble they were within historical norms. Besides, isn’t the sign of excessive money printing supposed to be rising inflation? We’ve had a whole generation of successive bubbles — and inflation is lower than it was at the beginning.

O.K., the other obvious culprit is financial deregulation — not just in the United States but around the world, and including the removal of most controls on the international movement of capital. Banks gone wild were at the heart of the commercial real estate bubble of the 1980s and the housing bubble that burst in 2007. Cross-border flows of hot money were at the heart of the Asian crisis of 1997-98 and the crisis now erupting in emerging markets — and were central to the ongoing crisis in Europe, too.

In short, the main lesson of this age of bubbles — a lesson that India, Brazil, and others are learning once again — is that when the financial industry is set loose to do its thing, it lurches from crisis to crisis.