The financial crisis also emboldened lawmakers and financial regulators. The Dodd-Frank financial reform legislation explicitly banned some of the trading activities that had been big in Stamford before the crisis. But the set of international banking rules that have had the single largest impact require banks to hold capital as a buffer against trading losses — rules broadly referred to as Basel III. A bank trading $100 billion of corporate bonds, for example, now needs to hold around $10 billion of capital, in comparison with the $3 billion to $5 billion it would have needed before the crisis. If the bank does not have the $10 billion in capital and wants to continue trading, it is required either to raise more money from shareholders or put aside more of its profits, with all the costs that entails. The riskier the products a bank is trading, the more capital it needs to put aside for each dollar of trading.

The desire by regulators to have banks trim their risky trading desks has had a particular impact at RBS because the bank’s bailout left the British government as the majority owner. RBS’s government-controlled board has pushed the company to focus more on its British operations for retail and corporate customers and less on the international trading floors.

At an industry conference in March, the RBS chief executive, Ross McEwan, said: “As we increasingly wave goodbye to some of the hangovers from our past, a new model will emerge that is set up to deliver sustainable returns from a much lower risk profile.” (A spokesman for RBS said the bank had no formal comment for this article.)

While international rules tried to reduce risks, scandals of other sorts popped up. A rogue trader in UBS’s London offices lost $2 billion in 2011, one of the first of many trading scandals to leap from bank to bank. There were allegations that traders at the large banks had colluded to manipulate the benchmark interest rate known as Libor. That gave way to the details of how traders at different firms conspired to fix the exchange rates between major currencies. RBS and UBS, along with most other large institutions, have ended up paying billions of dollars in fines in these cases.

RBS’s cuts are striking, but other banks are heading in the same direction. Morgan Stanley has slimmed down its trading desks and strengthened the Smith Barney wealth management business it acquired during the crisis. This spring, JPMorgan Chase talked about the strength of its less risky consumer bank at the same time that it outlined billions of dollars of new cuts in its investment bank. Even Goldman Sachs, the most storied Wall Street firm, has been looking to diversify by entering businesses like consumer lending. The latest quarterly financial results from the big banks — announced over the last two weeks — have underscored the continued drop in revenue from traditional trading businesses.